JPS598478Y2 - Open phase detection device - Google Patents

Description

[Detailed Description of the Invention] This invention relates to an open-phase detecting device that does not malfunction and is particularly suitable for controlling an induction motor using a differential between a driving force and a braking force.

If the power supply circuit of a 3-phase induction motor has an open phase, it may not be able to start or there may be insufficient torque.Especially when driving an elevator, reverse torque will be generated due to the load, which may cause the elevator to reverse. Equipped with an open phase detection device to prevent

In addition to operating with an open phase, the open phase detection device generally has operating characteristics as shown in FIG. 1 when unbalanced.

That is, when the current i of at least one phase drops to the open phase level a at time T1, the operation is prepared, but there is a time delay of ΔT, and as shown in A, the operation is reset at T2 after the time ΔT has elapsed. When the current is larger than level b, it is determined that there is an open phase, and the open phase detection device operates.

On the other hand, as shown in B, if all three phases become smaller than the reset level b within the time Δτ, it is determined that there is an open phase and the open phase detection device does not operate.

In other words, it is designed not to operate in response to short-term current changes such as the interruption of a contactor.

In the conventional control of AC three-phase induction motors, the current does not normally drop below operating level A even if the si-risk is controlled, and when the current drops to zero, it does so in an extremely short time. The method was to move to

However, as the speed of AC elevators increases, instead of using the synchronous speed of the induction motor (Aa in Figure 2) during short floor operation, simultaneous excitation of the braking force and driving force results in an increase in speed as shown in Figure 2Ab. A method is used to obtain a predetermined speed.

At this time, if the braking force and driving force are pushed or pulled in order to reduce the energizing current and save power, for example, when an elevator is rising without load, the driving force is not required near the steady speed, and the control for the balance weight is performed. Controlled only by power.

When this is expressed in terms of current, the braking current IB is as shown in FIG. 2B, and the driving current IA is as shown in FIG. 2C, and the driving current gradually decreases and reaches zero near the end of acceleration.

Therefore, under the conditions shown in FIG. 1A, there is almost always a slight unbalance on both the power supply side and the load side, and the open phase detection device operates.

Even though this is not actually an open phase, is there a power supply itself or a load between each phase, and the detection times? It is determined that the phase loss is due to unbalance of the current transformer and the detection circuit itself, and since the time is longer than ΔT in FIG. 1, the phase loss detection device operates.

As a means to prevent this, it is possible to extend the operation delay time ΔT of the open phase detection device or to reduce the hysteresis of the operation level, but in the former case, the following problem occurs in the elevator.

That is, when one phase is open in the circuit shown in FIG. 3, the current becomes single-phase, and the induction motor 1 does not generate starting torque, resulting in insufficient torque.

On the other hand, since the electromagnetic brake 16 can open, for example, in a no-load descending operation, the electromagnetic brake 16 may be reversed due to an unbalanced load with respect to the balance weight 19, which is disadvantageous.

There is a limit to reducing the latter operating level due to switching stability.

The purpose of this invention is to eliminate the drawbacks of the above-mentioned conventional techniques and to detect an open phase state with high precision at all times during operation of an induction motor in a device that drives an induction motor using an AC power source and brakes it with DC power. is to provide.

The feature of this device is that a current transformer is inserted into each phase of the AC power line that supplies power to the induction motor to detect an open phase. At least one of the AC power supply lines is inserted into the primary side of each phase of each of the current transformers in parallel with the AC power supply inserted into the primary side.

This makes it possible to stably and accurately detect any open phase state during operation of the induction motor.

This invention will be explained in detail below with reference to an embodiment shown in FIG.

The induction motors 1 and 2 may have drive shafts directly connected to each other, or may be pole-switching motors having a common rotor.

The induction motor 1 includes anti-parallel thyristors 3, 4, operating direction switching contactors 81, 82 (upward operation) and 91. 92
(downward operation) to supply three-phase AC R, S, T.

On the other hand, direct current is supplied to the induction motor 2 via the rectifier bridge 5 and the brake circuit contactors 61 and 62.

The induction motors 1 and 2 include a hoisting groove wheel 17 and a rope 2.
An elevator car 18 and a balance weight 19 are connected via 0.

On the other hand, a speed detector 14 is connected to detect the shaft rotation speed of the induction motors 1 and 2, and a phase shifter 22 is operated according to the deviation from the speed reference command 15.

A current negative feedback circuit is formed in the phase shifter 22 by the current transformer 21 which detects the braking circuit current.

the anti-parallel thyristor 3 according to the output of the phase shifter 22;
, 4, drive the thyristor of the rectifier bridge 5.

Note that the phase shifter 22 does not necessarily represent one phase shifter, but has a phase shifter corresponding to each pair of thyristors,
The phase shifter group is indicated by 22.

The above is an example of a speed control system, and the gist of the present invention does not change for other current control systems or voltage control systems.

In the above structure, for example, when the power supply of any one of the R phase, S phase, and T phase becomes open phase, or when thyristor 3 or 4 has an oven failure, the current is changed to detect the open phase. An open phase detection device consisting of circuits 71, 72, 73 and an open phase detection circuit 10 is provided.

On the primary side of the current transformers 71 to 73, AC lines corresponding to the R, S, and T phases, respectively, and the AC side power supply line 11 of the rectifier bridge 5 are connected to each phase.

Further, an electromagnetic brake 16 is connected to the load side of the driving direction switching contactor via a rectifier circuit 24, and is configured to apply braking torque to the shafts of the induction motors 1 and 2.

In such a structure, when the direction of operation of the elevator car 18 is determined in response to a call, the contactors 81 and 82 are turned on, for example, in an upward operation.

As a result, the electromagnetic brake 16 opens, the induction motor 1 generates a starting torque according to the phase of the thyristors 3 and 4, and the elevator car 18 is operated in a predetermined direction according to the call.

However, if, for example, the R phase is open, the induction motor 1 has no starting torque, so if the elevator is operating at full load, the elevator car 18 side is heavier than the balance weight 19, so the elevator car 18 side is heavier than the balance weight 19. On the contrary, the car 18 descends.

Since this is inconvenient and unsafe, in the case of a phase failure, the phase failure detection circuit 10 is activated and the operation direction switching switch 8 is activated.
1 and 82, and the electromagnetic brake 16 holds the elevator.

Next, a case will be described in which the elevator accelerates under normal conditions and the anti-parallel thyristors 3 and 4 and the rectifying bridge 5 are simultaneously controlled at a speed lower than the synchronous speed of the induction motor 1 to perform, for example, no-load upward operation.

In this case, in order to maintain a predetermined speed, the load torque acts to accelerate the elevator car 18, so motoring torque is not necessary, but braking torque is required.

Since the speed is lower than the synchronous speed, no dynamic braking torque can be applied, so the motor current is throttled as shown in FIG. 2C, and a DC braking current IB is caused to flow as shown in FIG. 2B.

At this time, the motor current IA gradually decreases to zero, so that it may not reach the reset level b within the predetermined operation delay time ΔT after entering the set level a of the open phase detection device shown in Fig. 1. .

For this purpose, the second
A control current IB shown in FIG. B is supplied to current transformers 71 to 73.

As a result, the period during which the braking current is flowing is equivalent to a state in which the three-phase power supply is valid, and the open phase detection device does not malfunction.

If we consider the case where the R phase becomes an open phase, this is a region where no motor current is originally flowing, and the operating state will not change in any way.

In this case, the open phase will be detected at the next startup to protect against single phase abnormality.

When the S phase and T phase are open, the open phase detection device is activated to stop the elevator.

This invention has the effect that it is possible to economically and reliably prevent malfunctions of the open phase detection device, and that abnormalities due to open phases can be prevented without any problems.

FIG. 4 shows an embodiment in which the present invention is applied to a three-phase full-wave DC braking circuit, in which each of the three-phase feeder lines 11 to 13
are connected to current transformers 71 to 73 to obtain the same effect as shown in FIG.

In addition, when the current transformers 71 to 73 of the open phase detection device are used as the power supply side of the operating direction switching contactors 81, 82; 91, 92, the current transformers 71 to 73 are simply connected to the rectifier bridge circuit at , q, and r should be provided on the power supply side.

[Brief explanation of drawings]

Figure 1 is a diagram of the operating characteristics of the open phase detection device in unbalanced conditions, Figure 2 is a diagram of the speed and current characteristics of the induction motor when it is lower than the synchronous speed, and Figure 3 is a circuit diagram showing an embodiment of this invention. 4 is a circuit diagram showing another embodiment of this invention. 1, 2... Induction motor, 3, 4... Anti-parallel sirisk, 5... Rectifier bridge, 10... Open phase detection circuit,
11-13... AC side power supply line, 16... Electromagnetic brake, 18... Elevator car, 19... Balance weight,
21... Current transformer, 22... Phase shifter, 61, 62.
...Brake circuit contactor, 71-73...Open phase detection current transformer, 81-82...Operation direction switching contactor, 91, 92
... Operating direction switching contactor, R, S, T...3
Phase AC power supply.

Claims (1)

[Scope of utility model registration request] An induction motor, this induction motor drive circuit, an open-phase detection device that has a current transformer inserted in each phase of an AC power line that supplies power to this induction motor drive circuit, a rectifier circuit that constitutes a DC braking circuit for the induction motor, and this and an AC power supply line connected to the AC side of a rectifier circuit, and in which the motor is driven and braked by the drive and rectification circuit, at least one of the AC power supply lines is connected to each phase of the current transformer. On the primary side,
An open phase detection device characterized by being inserted in parallel with the drive circuit AC power line.