JP2003219577A - Automatic switch for uninterruptible power unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an automatic switch for an uninterruptible power unit which can build the duplication of a power system without making the load stopped, and reduce the risk of load stoppage at switching between a normal power unit and a backup power unit, thereby enhancing the reliability. <P>SOLUTION: This automatic switch 10, for an uninterruptible power unit, which performs power supply to load 50 by switching the normal power unit 20 and the backup power unit 30 each equipped with uninterruptive power units, is equipped with a first switch 44a inserted into the input side of the commercial DC power source of the normal power unit and a second switch 44b, connected between the secondary side of this first switch and the output of the backup power source; and this is constituted so that the cut off or the cut back of the normal power unit is conducted by the on-off control of the first and second switches. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic switching device for an uninterruptible power supply, and particularly when it is necessary to disconnect the power supply due to a failure or inspection of the power supply, and when the power supply is turned off by a failure recovery or inspection completion. When it becomes necessary to return, you can always supply uninterruptible power to the load without connecting to the commercial direct power supply, and you can build a redundant power system at any time without load stop, and disconnect and switch back the backup power supply. The present invention relates to a technique for automatically switching an uninterruptible power supply that automatically performs the above.

[0002]

2. Description of the Related Art Conventionally, an automatic switching device for an uninterruptible power supply (hereinafter referred to as UPS) is disclosed in, for example, Japanese Patent Laid-Open No. 2000-99.
No. 212, and it is configured as shown in FIG. In FIG. 4, a UPS automatic switching device 100
Is a regular power supply 110 and a backup power supply 12
0 and an automatic switching unit 130.

The normal power supply device 110 is a UPS 111.
And an output changeover switch 112. Here, the UPS 111 is supplied with the power supply voltage from the regular UPS power supply 113. Further, the output selector switch 112 is configured such that the input side selectively switches between the UPS 111 and the commercial direct power source 114 without interruption, and supplies the UPS load side to the UPS load side.

The backup power supply device 120 is similarly composed of a UPS 121 and an output changeover switch 122. The UPS 121 is a backup U
A power supply voltage is supplied from the PS power supply 123. Also,
The input side of the output changeover switch 122 is the UP
S121 and the commercial direct-current power supply 114 are selectively switched without interruption and are supplied to the UPS load side.

Further, the automatic switching section 130 comprises a control section 131, an operating section 132, a display section 133 and an output changeover switch 134. Here, the control unit 131 detects whether there is a failure or inspection of the regular power supply device 110 and the backup power supply device 120, and outputs these output changeover switches 112, 1
The switching state of 22 and the switching state of the output changeover switch 134 are detected and the switching control is performed.

[0006] The operation unit 132 is designed to instruct disconnection and switching back and inspection of the backup power supply device 120. The display unit 133 is configured to display the states of both power supply devices 110 and 120 and the switching state of the switch 134. The output selector switch 134 includes two switches 134a and 134b.
The input side is connected to the outputs of the normal power supply device 110 and the backup power supply device 120, and the output side is connected to the UPS load 140.

According to the automatic switching device 100 for an uninterruptible power supply having such a configuration, normally, the output changeover switch 112 of the regular power supply device 110 is located on the UPS 111 side, and the switch 134a of the output changeover switch 134 of the automatic changeover unit 130. Are connected to the common power supply devices 110, respectively. As a result, the power supply voltage is applied from the regular UPS power supply 113 to the regular power supply 110, and the regular power supply 110
From the UPS load 140 to the output changeover switch 112 and the output changeover switch 134 of the automatic changeover unit 130.
The power supply voltage is supplied to.

Here, when a failure occurs in the regular power supply device 110 or inspection is required, the user operates the operation unit 132 of the automatic switching unit 130. As a result, the control unit 131 of the automatic switching unit 130 switches the output changeover switch 112 of the regular power supply device 110 to the commercial direct power supply 114, checks the output changeover switch 122 of the backup power supply device 120, and confirms the commercial direct power supply 114 side. If not connected, the output selector switch 122 is switched to the commercial direct power source 114 side. Then, the control unit 13
1 turns on the switch 134b of the output changeover switch 134, and further turns off the switch 134a. As a result, the normal power supply device 110 is switched to the backup power supply device 120.

After that, the control unit 131 switches the output changeover switch 122 of the backup power supply unit 120 to the backup UPS power supply 123 side. As a result, the backup UPS power supply 123 to the backup power supply 120
A power supply voltage is applied to the UPS load 140 from the backup power supply device 120 via the output changeover switch 122 and the output changeover switch 134 of the automatic changeover unit 130. With the above, the regular power supply device 1
Ten separations will be made.

Similarly, when the backup power supply unit 120 is switched back to the normal power supply unit 110 after the normal power supply unit 110 is recovered from the failure and the inspection is completed, the switchback work is performed in the reverse order of the above operation.

[0011]

However, the automatic switching device 100 for an uninterruptible power supply having such a configuration has the following problems. The first problem is UP
After starting the operation of the S load 140, the backup power supply 1
This means that the operation of the UPS load 140 needs to be temporarily stopped when the power supply system is duplicated by 20. This is because the regular power supply device 110 and the backup power supply device 120 are connected to the UPS load 140 in parallel with each other via the switches 134a and 134b of the output changeover switch 134, respectively. Therefore, for example, 24 such as a server
In the case of the UPS load 140 that cannot be stopped for 365 days, a dual power supply system cannot be constructed.

A second problem is that the normal power supply 110 and the backup power supply are disconnected when the normal power supply 110 is disconnected from the backup power supply 120 or when the backup power supply 120 is switched back to the normal power supply 110. In the device 120, since the output changeover switches 112 and 122 are once switched to the commercial direct power source 114, if the commercial direct power source 114 experiences a momentary voltage drop or a power failure, the UPS load 140 may stop. is there. This is because the regular power supply 110 and the backup power supply 120 are independently UP
This is because the S load 140 is connected in parallel.

A third problem is that, in the above-mentioned disconnection and switching back, the output changeover switch 1 in the normal power supply device 110 and the backup power supply device 120, respectively.
This means that the switching of the output changeover switches 112 and 122 is increased because the commercial direct power sources 114 and 122 are once switched, and the reliability of power supply to the UPS load 140 is reduced. This is the common power supply voltage 110 and the backup power supply device 1.
This is because the commercial direct power source 114 to be supplied to 20 is not backed up.

The present invention has been made to solve the above problems, and it is possible to build a dual power supply system without stopping the UPS load even after the operation of the UPS load that cannot be stopped is started. At the same time, it is an object of the present invention to provide a technique for automatically switching an uninterruptible power supply, which reduces the risk of a UPS load being stopped when switching between a regular power supply and a backup power supply and improves reliability.

[0015]

In order to achieve this object, an automatic switching device for an uninterruptible power supply according to claim 1 of the present invention comprises a normal power supply device and a backup power supply device each equipped with an uninterruptible power supply device. Is an automatic switching device for an uninterruptible power supply that switches power to the load by supplying the output of the service power supply directly to the load and to the input side of the commercial direct power supply of the service power supply. The inserted first switch, and the second switch connected between the secondary side of this first switch and the output of the backup power supply, the disconnection or reverting of the working power supply, The normal power supply device and the backup power supply device are configured to be controlled by on / off control of the first switch and the second switch without being switched to the commercial direct power supply.

When the automatic switching device of the uninterruptible power supply is configured as described above, the power is normally supplied from the regular power supply to the load, and the backup power supply is operated without load. In this state, if a failure or the like occurs in the commercial power supply device, the commercial power supply device switches to the commercial direct power supply side without interruption, and power is supplied from the commercial direct power supply side to the load. At this time, since the output of the backup power supply device is connected to the commercial direct power supply side of the regular power supply device, the backup power supply device supplies power to the load by the uninterruptible power supply.

Also, when switching back from the regular power supply unit to the backup power supply unit, similarly, the commercial direct power supply side of the regular power supply unit is switched to the UPS side, and the uninterruptible power supply from the regular power supply unit becomes a load. Will be supplied to. Therefore, when switching from the commercial power supply to the backup power supply or from the backup power supply to the commercial power supply, the commercial direct power supply does not supply power to the load, so the instantaneous voltage of the commercial direct power supply The interruption of power supply to the load due to deterioration or power failure will be completely eliminated.

Further, in a normal state in which power is being supplied from the regular power supply to the load, even if the commercial direct power supply side of the regular power supply is stopped, the power supply to the load is not affected. . Therefore, it is possible to connect the backup power supply unit and the automatic switching unit to the commercial direct power supply side of the regular power supply at any time while the commercial direct power supply side of the regular power supply is stopped. As a result, even after the operation of the load is started, it is possible to build a dual power supply system by connecting the backup power supply device and the automatic switching unit without interrupting the operation of the load.

An automatic switching device for an uninterruptible power supply according to a second aspect of the present invention is configured to include a control unit that controls switching of the first switch and the second switch. When the automatic switching device of the uninterruptible power supply has such a configuration, the control unit controls the switching of the first switch and the second switch, so that the commercial direct power supply side of the commercial power supply is commercialized. A direct power supply or a backup power supply will be connected accordingly.

In the automatic switching device for an uninterruptible power supply according to a third aspect of the present invention, the control unit detects the operating states of the regular power supply device and the backup power supply device and the switching states of the first and second switches. , Based on this detection status
The configuration is such that switching control of the first switch and the second switch is performed. If the automatic switching device of the uninterruptible power supply is configured in this way, the control section automatically switches the first and second switches automatically according to the operating states of the regular power supply and the backup power supply at that time. can do.

In the automatic switching device for an uninterruptible power supply according to claim 4, the control unit detects a failure state of the backup power supply apparatus, and based on this failure state, the first switch and the second switch. It is configured to perform switch switching control. When the automatic switching device of the uninterruptible power supply has such a configuration, the control unit can automatically switch the first and second switches as appropriate according to the failure state of the backup power supply at that time. .

An automatic switching device for an uninterruptible power supply according to a fifth aspect of the present invention is configured to include an operating unit for instructing the backup power supply to be disconnected or switched back and the backup power supply to be inspected. When the automatic switching device for the uninterruptible power supply has such a configuration, the user operates the operation unit to disconnect or switch back the backup power supply and to instruct the backup power supply to perform automatic switching. The device appropriately controls switching of the first switch and the second switch. As a result, the backup power supply device can be disconnected or switched back, and the backup power supply device can be inspected while being disconnected from the load.

An automatic switching device for an uninterruptible power supply according to claim 6 is provided with a display section for displaying the operating states of the regular power supply and the backup power supply and the switching states of the first and second switches. There is. When the automatic switching device of the uninterruptible power supply is configured as described above, the display section displays the operating states of the regular power supply unit and the backup power supply unit and the switching states of the first and second switches. By visually observing, it is possible to easily and visually confirm the operating states of the above-mentioned regular power source device and the backup power source device and the switching states of the first and second switches.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. First, an embodiment of an automatic switching device for an uninterruptible power supply according to the present invention will be described with reference to FIG. FIG. 1 is a block diagram showing the configuration of an automatic switching device for an uninterruptible power supply according to this embodiment.

As shown in FIG. 1, an automatic switching device 10 for an uninterruptible power supply comprises a regular power supply 20, a backup power supply 30, and an automatic switching section 40.

The normal power supply unit 20 includes a UPS 21 and
And an output changeover switch 22. The UPS 21 is supplied with a power supply voltage from a regular UPS power supply 23. The input side of the output changeover switch 22 is selectively switched between the UPS 21 and the commercial direct-current power supply 24 without interruption, and is supplied to the UPS load 50. Here, the UPS load 50 is required to be continuously operated for 24 hours 365 days, such as a server.

The backup power supply device 30 similarly comprises a UPS 31 and an output changeover switch 32. Here, UPS31 is a backup UPS
The power supply voltage is supplied from the power supply 33. Further, the output changeover switch 32 selectively switches the UPS 31 and the commercial direct power source 24 without interruption on the input side, and
It is designed to be supplied to the load side.

Further, the automatic switching section 40 is composed of a control section 41, an operating section 42, a display section 43 and an output changeover switch 44. Here, the control unit 4
Reference numeral 1 detects whether or not the normal power supply device 20 and the backup power supply device 30 have failed or inspected, and the output changeover switches 22 and 32 are changed over and the output changeover switch 44 is changed over. The failure signal of 30 and the inspection signal of the backup power supply device 30 from the operation unit 42 and the control signal for switching the backup power supply device 30 are transmitted, and these signals are also transmitted to the display unit 43.

The operation unit 42 sends a command signal for disconnecting and switching back, checking the backup power supply unit 30, and disconnecting and switching back the backup power supply unit 30 to the control unit 41 and the display unit 43. There is. The display unit 43 displays the power supply devices 20 and 30 for both the power supply devices 20 and 30 based on signals from the control unit 41 and the operation unit 42.
And the switching state of the switch 44 are displayed. The output changeover switch 44 is composed of two switches 44a and 44b.

The above-mentioned configuration is similar to the automatic switching device 100 of the uninterruptible power supply shown in FIG. 4, but the automatic switching device 1 of the uninterruptible power supply according to the embodiment of the present invention.
0 has a different configuration in the following points. That is, the first switch 44 a of the output changeover switch 44 is inserted in the power supply line from the commercial direct power supply 24 of the regular power supply device 20. The input side of the second switch 44b is connected to the output of the backup power supply device 30 and the output side is connected to the secondary side of the first switch 44a.

Next, the normal operation of the automatic switching device 10 of the uninterruptible power supply of this embodiment, and the disconnecting and switching back operations will be described below.

First, the normal operation will be described. During normal operation, the output changeover switch 22 of the regular power supply device 20
And the output changeover switch 32 of the backup power supply device 30 is changed over to the UPS 21, 31 side, respectively. Of the output changeover switches 44 of the automatic changeover unit 40, the first switch 44a is turned off and the second switch 44b is changed. It is turned on. As a result, the regular power supply 2
0 supplies power to the UPS load 50 by power supply from the regular UPS power supply 23. Further, the backup power supply device 30 is supplied with power from the backup UPS power supply 33 in preparation for backup of the regular power supply device 20,
It is operated without load.

Here, if a failure or the like occurs in the regular power supply device 20, the regular power supply device 20 will output the output changeover switch 22.
Switch to the commercial direct power supply 24 side without any interruption, and UPS21
Is disconnected from the power supply system. At this time, the commercial direct power supply 24 side of the output changeover switch 22 of the regular power supply device 20 is connected to the output of the backup power supply device 30 via the second switch 44b. The power is not supplied from 24, and the uninterruptible power supply by the UPS 31 from the backup power supply 30 is the output changeover switch 2 of the regular power supply 20.
2 via. Therefore, since the UPS load 50 is constantly supplied with uninterruptible power, the regular power supply 2
When the output changeover switch 22 of 0 is switched, the UPS load 50 due to an instantaneous voltage drop or power failure of the commercial direct power supply 24
Power outages to the power stations will be completely eliminated.

When switching from the backup power supply device 30 to the normal power supply device 20 due to failure recovery of the normal power supply device 20 or the like, the output changeover switch 22 is switched to connect to the commercial direct power supply 24 without interruption. It is switched to UPS21 without being performed.

Further, in a normal state in which the UPS 21 of the regular power supply unit 20 is supplying power to the UPS load 50, even if the commercial direct power source 24 side of the regular power supply unit 20 is stopped, the UPS load 50 is stopped. There is no impact on the power supply to As a result, the backup power supply device 3 is always ready for the commercial direct power supply 24 side of the regular power supply device 20 in a state where the commercial direct power supply 24 is stopped.
0 and the automatic switching unit 40 can be connected. Therefore, even after the operation of the UPS load 50 is started, it is possible to construct a dual power supply system by connecting the backup power supply device 30 and the automatic switching unit 40 without interrupting the operation of the UPS load 50.

Next, the automatic switching device 10 of the uninterruptible power supply device
The disconnecting operation in step 2 will be described with reference to the flowchart in FIG. In FIG. 2, the user operates the operation unit 4
When the inspection switch of the UPS 31 of the backup power supply device 30 is turned on by 2, the operation unit 42 sends an inspection signal to the control unit 41. Then, in step A1, the control unit 41 detects and determines the presence or absence of the inspection signal of the UPS 31 of the backup power supply device 30 from the operation unit 42.

Then, if there is no inspection signal in step A1, the control section 41 determines whether or not the UPS 31 of the backup power supply device 30 has a failure in step A2. UPS of the backup power supply 30 in step A2
When there is no failure in 31, the control unit 41 determines in step A3 whether the backup power supply disconnection switch is turned on. If the backup power supply disconnecting switch is not turned on in step A3,
Return to step A1.

On the other hand, if the backup power supply disconnecting switch is turned on in step A3, the control section 41 determines in step A4 the regular power supply device 2
The switching state of the 0 output selector switch 22 is determined.
Then, in step A4, when the output changeover switch 22 of the regular power supply device 20 is changed over to the UPS 21 side, the control section 41 turns off the second switch 44b of the output changeover switch 44 in step A5. After doing
At step A6, the first switch 44a of the output changeover switch 44 is turned on. In step A4,
When the output changeover switch 22 of the regular power supply device 20 is switched to the commercial direct power supply side, the control unit 41 switches the output changeover switch 32 of the backup power supply device 30 to the commercial direct power supply 24 side in step A7. After that, in step A8, the first switch 44a of the output changeover switch 44 is turned on, and then in step A9, the second switch 44b of the output changeover switch 44 is turned off.

If there is an inspection signal in step A1, the process proceeds to step A4, and if the output changeover switch 22 of the regular power supply device 20 is switched to the commercial direct power supply side, the control section 41 In step A7, the output changeover switch 32 of the backup power supply unit 30 is changed over to the commercial direct power supply 24 side, and in step A8, the first switch 44a of the output changeover switch 44 is turned on, and then the output changeover switch. 44 second switch 44b
Turn off. Accordingly, the backup power supply device 30 can be automatically disconnected from the regular power supply device 20 without switching the output changeover switch 22 of the regular power supply device 20. Furthermore, if the UPS 31 of the backup power supply 30 has a failure in step A2, the process proceeds to step A8, and the control unit 41 turns on the first switch 44a of the output changeover switch 44, and then in step A9. The second switch 44b of the output changeover switch 44 is turned off. This completes the disconnection operation.

Next, the automatic switching device 1 for the uninterruptible power supply device
The switching back operation at 0 will be described with reference to the flowchart of FIG. In FIG. 3, the automatic switching unit 4
Of the 0 output changeover switches 44, the first switch 4
4a is on and the second switch 44b is off, the user turns on the connection switch of the backup power supply device 30 with the operation unit 42. As a result, in step B1, the control unit 41 determines whether the connection switch of the backup power supply device 30 from the operation unit 42 is turned on. If the connection switch is not turned on in step B1, the process returns to step B1.

Then, when the connection switch is turned on in step B1, the control section 41 determines in step B1.
At 2, it is determined whether the output selector switch 32 of the backup power supply device 30 is switched to the UPS 31 side. At step B2, the output changeover switch 32 is up.
When it is switched to the S31 side, in step B3, the control unit 41 determines whether the output selector switch 22 of the regular power supply device 20 is switched to the UPS 21 side. In step B3, the output changeover switch 22 is up.
When switched to the S21 side, the control unit 41
At step B4, the first switch 44a of the output changeover switch 44 is turned off, and then at step B5, the second switch 44b of the output changeover switch 44 is turned on.

On the other hand, when the output selector switch 22 is switched to the commercial direct power source 24 side in step B3, the control section 41 determines the output selector switch of the backup power supply unit 30 in step B6. After switching 32 to the commercial direct power supply 24 side, in step B7, the second switch 44b of the output changeover switch 44 is turned on, and then in step B8, the first switch 44a of the output changeover switch 44 is turned off. Then, in step B9, the output changeover switch 3 of the backup power supply device 30
Switch 2 to UPS31 side.

In step B2, the output changeover switch 32 of the backup power supply unit 30 is turned on by the commercial direct power supply 2
If it has been switched to the 4th side, it is determined in step B10 whether or not there is a failure in the UPS 31 of the backup power supply device 30. Then, in step B10, UPS3
When the failure of No. 1 is detected, the process proceeds to step B1. On the other hand, if there is no failure of the UPS 31 in step B10, the control unit 41 sets the output changeover switch 32 of the backup power supply device 30 to U in step B11.
Switch to the PS31 side and proceed to step B3. Above,
The switching back operation is completed. As a result, the regular power supply 2
The UPS 31 of the backup power supply device 30 can be automatically switched back as the backup power supply of the regular power supply device 20 without switching the output selection switch 22 of 0.

In the above-described embodiment, one backup power supply device 3 is provided for one regular power supply device 20.
Although 0 is provided, the present invention is not limited to this, and two or more backup power supply devices may be provided.

[0045]

As described above, according to the present invention, normally, power is supplied from the regular power supply to the load, and the backup power supply is operated without load. In this state, if a failure or the like occurs in the commercial power supply device, the commercial power supply device switches to the commercial direct power supply side without interruption, and power is supplied from the commercial direct power supply side to the load. At this time, since the output of the backup power supply device is connected to the commercial direct power supply side of the regular power supply device, the backup power supply device supplies power to the load by the uninterruptible power supply.

Also, when switching back from the regular power supply to the backup power supply, similarly, the commercial direct power supply side of the regular power supply is switched to the UPS side, and the uninterruptible power supply becomes a load from the regular power supply. Will be supplied to. Therefore, when switching from the commercial power supply to the backup power supply or from the backup power supply to the commercial power supply, the commercial direct power supply does not supply power to the load, so the instantaneous voltage of the commercial direct power supply The interruption of power supply to the load due to deterioration or power failure will be completely eliminated.

Further, in a normal state in which power is being supplied from the regular power supply to the load, even if the commercial direct power supply side of the regular power supply is stopped, the power supply to the load is not affected. . Therefore, it is possible to connect the backup power supply unit and the automatic switching unit to the commercial direct power supply side of the regular power supply at any time while the commercial direct power supply side of the regular power supply is stopped. As a result, even after the operation of the load is started, it is possible to build a dual power supply system by connecting the backup power supply device and the automatic switching unit without interrupting the operation of the load.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of an automatic switching device for an uninterruptible power supply according to the present invention.

FIG. 2 is a flowchart showing a disconnecting operation in the automatic switching device of the uninterruptible power supply of FIG.

3 is a flowchart showing a switching back operation in the automatic switching device of the uninterruptible power supply of FIG.

FIG. 4 is a block diagram showing a configuration of an example of a conventional automatic switching device of an uninterruptible power supply.

[Explanation of symbols]

10 Automatic switching device for uninterruptible power supply 20 Regular power supply 21 UPS (Uninterruptible Power Supply) 22 Output selector switch 23 Regular UPS power supply 24 Commercial direct power supply 30 backup power supply 31 UPS 32 output selector switch 33 Backup UPS power supply 40 Automatic switching unit 41 Control unit 42 Operation part 43 Display 44 Output selector switch 44a First switch 44b Second switch 50 UPS load (load)

Claims (6)

[Claims] 1. An automatic switching device for an uninterruptible power supply, which supplies power to a load by switching between a regular power supply and a backup power supply, each of which has an uninterruptible power supply. The output is supplied directly to the load, and is connected between the first switch inserted on the input side of the commercial power supply of the commercial power supply and the secondary side of this first switch and the output of the backup power supply. The second power switch and the second power switch are provided for disconnecting or switching back the normal power supply device without switching the normal power supply device and the backup power supply device to the commercial direct power supply, and turning the first switch and the second switch on and off. An automatic switching device for an uninterruptible power supply characterized by being controlled. 2. The automatic switching device for an uninterruptible power supply according to claim 1, further comprising a control unit that controls switching of the first switch and the second switch. 3. The first switch detects the operating states of the regular power supply device and the backup power supply device and the switching states of the first and second switches, and based on the detected states, the first switch. 3. The automatic switching device for an uninterruptible power supply according to claim 1 or 2, which controls switching of the second switch. 4. The control unit detects a failure state of a backup power supply device and controls switching of the first switch and the second switch based on the failure state. An automatic switching device for an uninterruptible power supply according to any one of 1 to 3. 5. The uninterruptible power supply according to claim 1, further comprising: an operation unit for disconnecting or returning the backup power supply and instructing inspection of the backup power supply. Automatic switching device. 6. The display unit according to claim 1, further comprising a display unit for displaying operating states of the regular power supply unit and the backup power supply unit and switching states of the first and second switches. Automatic switching device for the uninterruptible power supply described.