JPH0479208B2 - - Google Patents

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention is directed to a three-phase AC motor that prevents phase loss and phase inversion to prevent accidents such as damage due to phase loss and phase inversion. Regarding protective devices.

(Prior Art) It has been well known that there are open phase and anti-phase protection devices as protection devices used in three-phase AC electric circuits. For example, a conventional 3E relay has a protection device as shown in FIG. There is a device that uses a CR phase shift circuit in the open phase/antiphase detection circuit (December 25, 1975, Electrical Calculation (Special Issue) No. 548 (Volume 43, No. 16)
(Refer to pages 199 to 201 of 2013), this circuit type changes the phase depending on the frequency, so it will not function properly unless the frequency is fixed, and there is the inconvenience that it is dedicated to 50 Hz and 60 Hz respectively. However, if this is to be made into a dual-use type, a switching device that is difficult to handle must be separately provided, or else the detection function as a protection device must be allowed to deteriorate.

In addition, there are five patterns in which phase loss occurs in a three-phase circuit, as shown in Figure 5, of which (C)
In the case of a break in the motor windings, etc., as shown in Figure 2, the current flowing in the three-phase wiring becomes unbalanced and only causes a phase shift. It is necessary to detect and generate an output to protect the motor. However, with conventional zero-current detection type open-phase protection devices, open-phase detection was possible only when the current value of a certain phase could be considered to be zero, so it was not possible to detect open-phase conditions due to the above-mentioned unbalance. It has been impossible to completely protect the motor during phase loss.

Furthermore, in any of the above conventional examples, in order to detect the opposite phase using the current method, three current transformers are required because they judge the state of each phase individually, which poses an economical problem. Ta.

(Problems to be Solved by the Invention) The present invention has been made in response to the above-mentioned circumstances, and while using two current transformers, which is less than the conventional one, it can be used in any way without being affected by frequency fluctuations. By making it possible to reliably detect and protect against open phase and anti-phase caused by various types of abnormal phenomena, we provide an economical and highly reliable open-phase and anti-phase protection device. An object of the present invention is to extend the life of a phase-current motor.

(Means for Solving the Problems) For this purpose, the present invention has a three-phase AC power supply circuit and a three-phase AC motor M, as shown in FIG.
For example, any two phases of the three-phase wiring connecting
Current transformers _1-1 and _1-2 are provided for the phase and R phase, respectively.
While the phase current and R phase current can be detected individually,
Corresponding to the current transformers _1-1 and _1-2 , zero-cross pulse generation circuits _2-1 and _2-2 whose input terminals are respectively connected to the respective secondary terminals are provided, and the T-phase current,
Pulses (P _T1 ), (P _T2 )..., (P _R1 ), (P _R2 ) are generated in synchronization with the instantaneous value of each input current (sine wave current) of the R phase current reaching zero value in the process of changing. …(Second
(See Figures A and B) For example, a square wave pulse is emitted.

These zero cross pulse generation circuits _2-1 , _2-2
An arithmetic processing device such as a microcomputer consisting of an interface having an input terminal associated with the output terminal of the interface, a time measuring means 3 such as an electronic counter, and a calculating means 4 is provided, and the output terminal of the interface is connected to an output portion 5 such as a relay. It is connected to the three-phase AC motor M via a circuit.

The time measurement means 3 is a zero cross pulse generation circuit 2
When receiving pulses from _-1 , _2-2 , it determines the phase corresponding to the pulse, and in the case of pulses (P _T1 ), (P _T2 )..., T phase, pulses (P _R1 ), (P _R2 )... In this case, after determining the R phase, time is measured from the time when the selected reference phase, for example, the pulse for the T phase ( _P The elapsed time (t ₀ ) when P _R1 ) was sent, and
Thereafter, the elapsed time (t ₁ ) when the pulse (P _T2 ) corresponding to the reference phase (T phase) is emitted as half a cycle of the AC power supply passes is measured, and the time measurement result is sent to the calculation means 4. tell.

The calculation means 4 calculates the time corresponding to the phase angle (120°) that the other phase (R phase) has with respect to the reference phase (T phase) when the other phase (R phase) has a predetermined phase rotation (see Fig. 2 A). Allowable time difference (△t) corresponding to phase angle (e.g. 20°) corresponding to allowable current unbalance rate (e.g. 20%)
The positive phase time relationship that holds true between the time period in which the adjustment is made and the time equivalent to a half cycle of the three-phase AC power supply, as well as the phase angle (60°) that the other phase has when the phase rotation is opposite to the reference phase. ) is calculated by adding or subtracting the allowable time difference (△t) to the time period corresponding to the half cycle of the three-phase AC power supply, and calculates the antiphase time relationship that holds true between the time period corresponding to the time _{corresponding} to , (t ₁ )
The time measuring means 3 calculates whether or not the numerical relationship between satisfies the positive phase time relationship every time it measures time, and if the positive phase time relationship does not hold, further establishes the antiphase time relationship. If the anti-phase time relationship is satisfied, an anti-phase signal is generated, and if the anti-phase time relationship is not established, a loss signal is generated due to a disconnection of the phase in which the current transformers _1-1 and _1-2 are not interposed. The phase signals are transmitted to the output section 5 by respectively transmitting phase signals. In addition, in determining the success or failure of the above-mentioned positive phase time relationship, it is possible to check the next antiphase time relationship only when ``failure'' occurs a set number of times in a row, or immediately after a single ``failure''. It's okay.

Next, when the output unit 5 receives the anti-phase signal or the open-phase signal, it outputs an output for opening the electromagnetic switch 6 for the motor M, and
In addition, even after the set time corresponding to several cycles of alternating current has elapsed, there is no pulse transmission from the zero-cross pulse generation circuit _2-1 related to the reference phase (T phase), and the counter-period equivalent time (t ₁ ) is counted. If not, it is assumed that an open phase has occurred in the reference phase (T phase), and an output is similarly generated to open the electromagnetic switch 6.

(Function) With the above configuration, the present invention can detect phase loss and anti-phase in all cases and take measures to protect the motor, and can fully achieve the intended purpose.

(Embodiments) Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Fig. 4 is a block diagram of the open-phase/out-of-phase protection device, which is a current transformer installed in the T-phase and R-phase wiring of the 3-phase wiring that connects the 3-phase AC motor M and the 3-phase AC power supply circuit. transformers _1-1 , _1-2 and their current transformers _1-1 , 1
- Zero cross pulse generation circuit 2 compatible with _2-
1 , _2-2 , and an electromagnetic switch 6 for the three-phase AC motor M.
an interface 7 that receives a signal (S ₁ ) that is transmitted in response to input of the signal, and an AND circuit that takes the logical product of the signal (S ₁ ) and the pulse (P _T ) of the zero-cross pulse generation circuit _2-1 . _8-1 and the signal (S ₁ )
and the pulse of zero cross pulse generation circuit _2-2 (P _R )
_An AND circuit _{8-2 that} calculates _the logical product _with an interface 9 comprising an output port (O ₁ ) for sending signals and a main port (O ₀ ) for sending anti-phase signals to the output unit 5; a power supply circuit 10 for supplying constant DC voltage to each part; a clock circuit 11 for configuring the time measurement means 3 and the calculation means 4;
Central processing unit consisting of CPU 12, ROM 13, and RAM 14, OR circuit 15, and driver 16-1 to _1
6-3 , open phase indicator _17-1 , anti-phase indicator _17-2 ,
The output unit 5 includes an output relay 18 for controlling the electromagnetic switch 6, and the electromagnetic switch 6 is turned on to energize the three-phase AC motor M as an input signal to the central processing unit. There are three signals: a signal (S ₁ ) that sends out a signal (S ₁ ), and the output of AND circuits _8-1 and _8-2 . On the other hand, the signal (S ₁ ) is being transmitted, and one of the zero-crossing pulse generation circuits _2-1 and _2-2 is transmitting a pulse, so that the input port (I ₀ ), A signal is input to one side of (I ₁ ), and an arithmetic processing command is sent to the central processing unit.

As will be made clear in the operation description below, when the central processing unit outputs an open-phase signal or an anti-phase signal, if an open-phase signal is output, the drivers _16-1 , 16- ₂ is activated and the open phase indicator _17-1 lights up to indicate an open phase, and at the same time, the output relay 18 is energized and the electromagnetic switch 6 is activated.
is opened, and the three-phase AC motor M is disconnected from the power supply and stopped. On the other hand, when the anti-phase signal is the main power, the drivers _16-2 and _16-3 are activated and the anti-phase indicator _17-2 is turned on. At the same time that the reverse phase is displayed, the output relay 18 is energized, and the three-phase AC motor M is operated to be disconnected from the power source and stopped.

By the way, to explain in principle how the above-mentioned protection device operates in order to detect anti-phase and open phase states, with reference to Fig. Zero-cross pulses are generated from the outputs of the circuits _1-1 and _1-2 by zero-cross pulse generation circuits _2-1 and _2-2 and input to the central processing unit.

The timekeeping means 3, for example, an electronic counter, is started by the zero-cross pulse (P _T1 ) of the T phase selected as the reference phase, and the zero-cross pulse generation circuit _2-2 associated with the current transformer _1-2 provided in the R phase generates a zero-cross pulse. When the pulse (P _R1 ) is generated, the elapsed time (t ₀ ) is measured and stored in the calculation means 4.

Furthermore, the electronic counter measures the elapsed time (t ₁ ) when the next zero-crossing pulse (P _T2 ) occurs in the T phase, and stores it in the calculation means.

Unless there is a phase loss or an abnormal unbalanced state on the power supply side or the motor M winding side, the phases of the T-phase and R-phase output signals (zero-cross pulses) will have a certain relationship, and the phase When the rotation is normal in a predetermined direction, the half-cycle equivalent time (t ₁ ) corresponding to 180 degrees in electrical angle and the elapsed time at the time of signal generation in the R phase with a difference of 120 degrees in electrical angle (t ₂ = t ₀ ), the relationship t ₂ = 2/3t ₁ holds true, and when the phase rotation is in the opposite direction, the signal generation time in the R phase with a 60° electrical angle difference is The relationship t ₃ =1/3t ₁ holds true with the elapsed time (t ₃ =t ₀ ).

This condition is when maintaining an equilibrium state in three-phase rotation, and for example, the voltage unbalance rate is 2%.
If the current unbalance rate is allowed up to 20% (to enable detection even under no-load conditions), the current unbalance rate will be approximately 20% (see Figure 3), and the phase angle deviation between the phases up to this unbalanced state is assumed to be acceptable. We calculated the phase angle tolerance and found that it was approximately 20°.

Therefore, the time (△t) corresponding to this allowable phase angle
△t=20/360×t ₁ =1/18・t ₁ Each of the above times t ₂ , t ₃
If the range of the value added or subtracted from is in the range of positive phase or anti-phase, and if it is in any other region, it is natural that there is an open phase (other than when a certain phase becomes completely zero current). This is a lack of phase in a broad sense, including the following.

Therefore, it is normal within the range of positive phase time relationship expressed by the formula t ₂ −△t≦t ₀ ≦t ₂ +△t, and t ₃ −△t≦t ₀
Since it is antiphase within the range of the antiphase time relationship shown by the formula ≦t ₃ + △t, and out of phase otherwise, calculations based on both of the above formulas were performed by the calculation means 4, and the result was obtained. Therefore, an anti-phase signal or an open-phase signal may be generated.

Incidentally, when an open phase occurs in the T phase, which is the reference phase, a start command is not issued to the timing means 3, so this is treated as an open phase state.

However, as mentioned above, there are two types of open phase patterns: open phase on the power supply side and open phase on the motor side.
Phase loss on the power supply side is classified into five types as shown in C and D and E, respectively.

Assuming that there is a disconnection at the x mark in line B in Figure 5A, if current transformers are installed in lines A and C, the phase angle between the A and C phases is 180°, an opposite phase, so it is considered as an open phase. If current transformers are provided in lines A and B or lines B and C, the B phase is at zero potential, so it can be detected as an open phase.

Also in FIG. 5B, the open phase can be detected for the same reason as in FIG. 5A, except that the motor connections are star-shaped and triangular.

In Figure 5 C, even if a current transformer is installed in any two phases of lines A, B, or C, there is a phase shift as is clear from the vector diagram, which indicates whether the phase is normal or out of phase. It is possible to detect an open phase by assuming that the conditions for

In Figure 5 D, if current transformers are installed in lines A and B or lines A and C, the A and B phases and the A and C phases are all in opposite phases, as is clear from the vector diagram. On the other hand, if current transformers are provided in lines B and C, this can also be detected as an open phase because the B and C phases are in phase.

In addition, in FIG. 5E, the only difference is that the motor connections are star-shaped and triangular, and an open phase can be detected for the same reason as in FIG. 5D.

As described above, it is possible to detect open phase and antiphase in all cases.

FIG. 6 shows the operation of the timer means 3 _and calculation means 4 in the protective _device that performs the above-mentioned detection and protection operation. , that is, the reference phase (T phase)
The timing means 3 determines whether or not the zero-cross pulse (P _T1 ) has been received (a), and if it has not been input, repeats check instructions (b), (c), and (d) synchronized with the transmission of the clock pulse. Based on this, it is determined whether there is a signal input (a), and the set number of times (N ₁ ) is determined.
In other words, if it is determined (d) that the pulse signal (P _T1 ) is not input even after performing a number of checks corresponding to a time of about 0.5 to 3 seconds, the output port (O ₁ )
(Y) and outputs the phase loss signal to the port (O ₁ ).
Emit from (re). This means an open phase in the T phase.

On the other hand, the pulse signal (P _T1 ) is input to the input port (I ₀ ).
If it is judged (a) that the input was made in the time measurement means 3,
At the same time as starting (e), read the input port (I ₁ ) and check whether the pulse signal (P _R1 ) is input or not.
In other words, it is determined (f) whether the zero-cross pulse (P _R1 ) of the other phase (R phase) is received, and if it is not input, the judgment is made based on the repeat check instructions (b), (c), and (d). Repeat f) and judge that there is no pulse signal ( _PR1 ) input even after 0.5 to 3 seconds have passed (d).
Then, the output port (O ₁ ) is output one after another (Y), and an open phase signal is emitted from the output port (O ₁ ). This is R
It means a lack of phase.

If it is determined that the pulse signal (P _R1 ) has been input midway through, the timer 3 reads the time (t ₀ ) at that time and stores the time (t ₀ ) in the register ( to).

Next, the input port (I ₀ ) is read and it is determined whether the pulse signal (P _T2 ) has been input (ch). Repeat the judgment (H) for 0.5 to 3 seconds, and when it is determined that there is no input (D), read the output port (O ₁ ) and (Y) output the open phase signal to the port (O ₁ ).
emanate from. This means that an open phase of the T phase has occurred.

When it is determined that the pulse signal (P _T2 ) has been input by the time the pulse signal (P T2 ) reaches 0.5 to 3 seconds, the clock means 3 is stopped, and the time (t ₁ ) is stored in the register and the clock is started. Clear means 3 (li).

Next, the formula for the positive phase time relationship is calculated using the calculation means 4.
t ₂ −△t≦t ₀ ≦t ₂ +△t, that is, 11/18t ₁ ≦t ₀ ≦13/
18 Perform calculation to determine whether the condition of t ₁ is satisfied or not.
(nu).

If it is determined that this calculation result satisfies the condition (NO), then it is normal, neither phase inversion nor phase loss, so the counter (J) that counts the number of calculations of the calculation means 4 is reset (NO) and the operation is performed again. The timing and arithmetic processing of (a) to (j) are performed every cycle.

On the other hand, if it is determined that the calculation result does not satisfy the condition (J), the counter (J) is counted by one (W) and the timing and calculation processes of (A) to (J) are repeated again.

As a result of the condition continuing to be unfulfilled, it is determined that the count number of the counter (J) has reached the set number of times (N ₂ ), and then the calculation means 4 calculates the antiphase time relationship equation t. ₃ - Δt≦t ₀ ≦t ₃ +Δt, that is, a calculation is performed to determine whether the condition of 5/18t ₁ ≦t ₀ ≦7/18t ₁ is satisfied (f).

When it is determined that the result of this calculation satisfies the condition (f), the output port (O ₀ ) is read out (t), and an inverted signal is emitted from the output port (O ₀ ) (s).

On the other hand, if it is determined that the condition is not satisfied,
The output port (O ₁ ) is read (Y), and the open phase signal is emitted from the output port (O ₁ ) (R).

Thus, based on the transmission of the open-phase signal (R) and the transmission of the anti-phase signal (S), the output section 5 generates an output for stopping the three-phase AC motor M (T).

The embodiment described above measures the elapsed time (t ₀ ) and (t ₁ ), sets the elapsed time (t ₁ ) as the reference, and sets the condition when the elapsed time (t ₀ ) is in positive phase. This is a method that calculates whether or not the condition is met, and whether the condition is met in the case of antiphase, but another method is to calculate the next pulse generation based on the elapsed time (t ₀ ). Calculate a prediction of what the elapsed time measured by the clock will be in positive and negative phase, and then compare the actual elapsed time with this predicted value to find out the correct value. It is also possible to distinguish between phase, antiphase, and open phase, and the effect is substantially the same as that of the above embodiment. The only difference is the calculation procedure in the calculation processing section.

The operation in this example will be explained with reference to FIG. 2 and FIG. 7. In FIG. 7, parts having the same functions as in FIG. There is.

R with the point of occurrence of the T-phase zero cross pulse ( _P
Based on the elapsed time (t ₀ ) until the phase zero-crossing pulse (P _R1 ) occurs, and assuming that the phase rotation is in a positive phase, the elapsed time of the next pulse (P _T2 ) to be generated is The predicted time value (t' ₂ ) would be 3/2t ₀ , whereas if it were antiphase, the predicted elapsed time value (t' ₃ ) would be 3t ₀ .

The accuracy can be determined by comparing these predicted values (t' ₂ ), (t' ₃ ) and the actually measured elapsed time (t ₁ ) taking into account the allowable time difference (△t) obtained from the current imbalance rate. It is possible to distinguish between phase, antiphase, and open phase, and the condition of 3/2t ₀ −△t≦t ₁ ≦3/2t ₀ +△t is satisfied and is normal, and 3t ₀ −△t≦t ₁ It is clear that the condition of ≦3t ₀ +△t is satisfied and there is an antiphase, and when neither condition is satisfied, it is an open phase.

Therefore, in FIG. 7, the pulse signal ( _PR1 )
is input to the input port (I ₁ ) and the elapsed time (t ₀ ) is stored in the register (g), then α = 3/2 (1-20/360) t ₀ and β = 3/2 (1 + 20/ 360) Perform the operation of t ₀ (ツ)
, Then, the elapsed time (t ₁ ) storage and timing means 3
When cleared (ri), the calculation α≦t ₁ ≦β is performed (nu′).

If this calculation result determines that the condition is satisfied (N'), it is normal; if it is determined that the condition is not satisfied (N'), it is determined that this unsatisfied state continues for the set number of times (N ₂ ). , and further causes the calculation means 4 to calculate 2α≦t ₁ ≦2β (f').

If the condition is met as a result of this calculation, an inverse phase signal is emitted from the output port (O ₀ ) (S), and if the condition is not met, an open phase signal is output from the output port (O ₁ ).
Emit from (re).

In this way, detection of positive phase, antiphase, and open phase is completely accomplished.

FIG. 8 is a flowchart according to yet another embodiment, which basically performs the same type of calculation as in the case of FIG. 7.

As explained in the case of _{FIG .} When the time measurement (t) reaches α, check whether a pulse signal is input to the input port (I ₀ ). If there is an input, it is normal, and if there is no input, the time measurement (t) has reached β. By the way, it is checked whether a pulse signal is input to the input port (I ₀ ), and if there is an input, it is normal, and if there is no input, it is determined that it is not normal, and the process moves to the next step (N) to (M).

The above processes (N) to (M) are the parts for determining whether the phase is correct or not.

Next, when the timer (t) reaches 2α, a check is started to see if a pulse signal has been input to the input port (I ₀ ). ) On the other hand, if there is no input, it continues to check whether a pulse signal has been input to the input port (I ₀ ) repeatedly until the clock (t) reaches 2β (O), and if there is an input, the check is performed repeatedly until the clock (t) reaches 2β. Assuming that it is a phase, count the number of times (W), and when the predetermined number of times (N ₂ ) is reached, an inverse phase signal is emitted from the output port (O ₀ ) (S), and when the time measurement (t) reaches 2β. If no pulse signal is input to the input port (I ₀ ),
When this continues a predetermined number of times (N ₃ ), an open phase signal is generated from the output port (O ₁ ).

The above processes (c) to (e) are the parts for determining whether phase is antiphase or phase is absent.

In this way, detection of positive phase, reverse phase, and open phase and protective operation are reliably performed.

(Effects of the Invention) Next, the effects of the present invention are as follows.

() Normal phase, anti-phase, and open phase are determined by relative comparison of the elapsed time equivalent to half a cycle of the reference phase (t ₁ ) and the elapsed time based on the phase angle between the two phases (t ₀ ). 50, so accurate detection is possible even if there are fluctuations in the power supply frequency.
Can be used in both 60Hz ranges.

() Since only two current transformers are required, equipment cost is reduced.

() No matter what the conditions are for antiphase or lack of phase,
Furthermore, it is possible to reliably detect abnormalities caused by unbalance such as voltage unbalance and disconnection of motor windings by measuring the two types of elapsed times (t ₀ ) and (t ₁ ). Therefore, it is possible to provide complete protection against abnormalities and provide a highly reliable protection device.

() If a method is adopted in which the allowable time difference (Δt) can be set externally, the allowable current unbalance rate can be easily varied, and appropriate protection without malfunction can be obtained in accordance with the power supply conditions.

() Distorted waveforms (including harmonics) are not affected and reliable detection is possible.

[Brief explanation of drawings]

Figure 1 is a block diagram showing the configuration of the present invention, Figure 2 is a block diagram showing the configuration of the present invention.
Figures A and B are explanatory diagrams of the operating principle of the device of the present invention, Figure 3 is a voltage unbalance rate-current unbalance rate relationship diagram, Figure 4 is a schematic structural diagram of an example of the device of the present invention, and Figure 5 is ~E are diagrams of open-phase patterns in a three-phase circuit, Figures 6 to 8 are flow diagrams showing the operation of the arithmetic processing unit in each example of the device of the present invention, and Figure 9 is a diagram of open-phase and anti-phase patterns in a conventional three-phase circuit. This is a detection circuit in a protection device. _1-1 , _1-2 ... Current transformer, _2-1 , _2-2 ... Zero cross pulse generation circuit, 3... Timing means, 4...
...Arithmetic means, 5...Output section, M...3-phase AC motor.

Claims (1)

[Claims] 1 Current transformers 1-1, 1-2, and both current transformers ₁ , respectively _, interposed in arbitrary two-phase wiring of the three-phase wiring that connects the three-phase AC current circuit and the three-phase AC motor M. ₋₁ ,
A zero-cross pulse generation circuit _2-1 that connects the input end to each secondary side terminal in correspondence with _1-2 and emits a pulse in synchronization with the instantaneous value of the input power supply becoming zero value in the process of change. , _2-2 , and zero-cross pulse generation circuits _2-1 , _2-2 , the phase corresponding to the pulse is determined, and from the time when the selected reference phase pulse is emitted, The time is measured, and the elapsed time (t ₀ ) when the next pulse is emitted from another phase other than the reference phase, and after that, the pulses for the reference phase are emitted as half a cycle of the AC power supply passes. Elapsed time (t ₁ )
and an allowable time difference (corresponding to a phase angle corresponding to an allowable current unbalance rate) to a time corresponding to a phase angle that the other phase has when the phase rotation is normal with respect to the reference phase. △t) and the time period equivalent to a half cycle of the three-phase AC power supply, as well as the phase angle that the other phase has when the phase rotation is opposite to the reference phase. Calculate the antiphase time relationship that holds between the time period obtained by adding or subtracting the allowable time difference (Δt) to the corresponding time and the time equivalent to a half cycle of the three-phase AC power supply, and calculate the elapsed time (t ₀ ), ( _t1 ) is calculated to determine whether or not the positive phase time relationship holds true each time the clocking means 3 measures time, and if the positive phase time relationship does not hold, the negative phase time relationship is determined. If the anti-phase time relationship is satisfied, an anti-phase signal is generated, and if the anti-phase time relationship is not established, the current transformers _1-1 , _{1-2 are} output.
a calculation means 4 for respectively transmitting an open phase signal caused by a disconnection of a phase that is not interposed; and the above-mentioned anti-phase signal or the above-mentioned open-phase signal sent by this calculation means 4, or equivalent to several cycles of an AC power supply. and an output section 5 for protecting the three-phase AC motor M by a phase-opening signal generated when the elapsed time (t ₁ ) is not counted even after a set time elapses. Phase protection device.