JPS5915229Y2 - Current limiting starting device - Google Patents

Description

[Detailed description of the invention] The present invention relates to a current-limiting starting device for a load that has starting characteristics such that the current is large at startup and gradually decreases over time, and reaches a steady value after a predetermined period of time. After a predetermined period of time, when the current reaches a steady value,
The load current detection device short-circuits the current-limiting resistor, and in the event that the load current detection device fails, the current-limiting resistor is short-circuited by the operation of an overcurrent relay connected in series with the current-limiting resistor. When the short-circuiting electromagnetic contactor fails, the contacts of the electromagnetic contactor close to enable continuous energization.

Hereinafter, one embodiment of this invention will be explained with reference to a diagram. In the diagram, E is a power source, NFB is a power supply breaker, CT is a current transformer, CR is a current detector connected to this current transformer CT, and CR-
b is a normally closed contact that opens after a predetermined time due to the current detected by the current detector CR; 88 is a normally closed magnetic contactor;
8-bl is the normally closed main contact of this electromagnetic contactor 88, 88-
b2 is another normally closed contact of the electromagnetic contactor 88, R is a current limiting resistor provided by bypassing the electromagnetic contactor 88, 49 is an overcurrent relay connected in series with the current limiting resistor R, 49- a
and 49-b are normally open and normally closed contacts of this overcurrent relay 49, 49T is a timer, 49T-a is a delay operation contact of this timer 49T, SHT is a tripping coil of the power breaker NFB, OL is a warning display lamp, and L is a load.

Next, the operation of the current-limiting starting device with the above configuration will be explained. Now, when voltage is applied to the power supply E side, the normally closed contact 49-b of the overcurrent relay 49 and the normally closed contact CR- of the current detector CR The electromagnetic contactor 88 is excited through b, and its main contact 88-bl is opened.

do.

When a load is connected in this state, current flows through the power source E, the breaker NFB, the current limiting resistor R1, and the overcurrent relay 49, and is limited by the current limiting resistor R.

Further, when a load is connected, the current instantaneously rises from zero to the maximum value at the time of starting, and during this rise, it assumes the value set on the current detector CR.

The current detector CR operates when it detects this value via the current transformer CT, and opens the normally closed contact CR-b after a predetermined time sufficient for the load current to reach a steady value.

As a result, the electromagnetic contactor 88 is de-energized, the normally closed main contact 88-bl of this electromagnetic contactor 88 is closed, and the current limiting resistor R
and the overcurrent line electric device 49 is short-circuited.

Note that the current setting value is set to be slightly smaller than the current during steady operation, and for a predetermined period of time, after the starting current returns to the steady value, the normally closed main contact 8 of the electromagnetic contactor 88 is
8-11 is set to close.

In the above circuit, when the current detector CR fails and does not operate, the overcurrent relay 49 is operated by the starting current, and its normally closed contact 49-b is opened after a predetermined time.

Therefore, the excitation of the electromagnetic contactor 88 is released and the main contact 88
-bl is closed, and the resistor R is short-circuited regardless of whether the current detector CR is operated or not.

This allows continuous energization of the load current, which takes a steady value.

However, even if the electromagnetic contactor 88 is de-energized by the operation of the overcurrent relay 49, the main contact 88-bl may not close due to a failure, and in that case, the current limiting resistor R is protected. There is a need.

This is because the current limiting resistor R generally only needs to be able to withstand the application of the starting current for a short period of time, and therefore has a small capacity.

Therefore, in that case, the closed contacts 49-a, 8
The breaker is activated after the set time of the timer 49T by the action of the timer 49T, which is excited via the timer 8-b2, and the tripping coil SHT of the breaker NFB, which is excited by the closing of the contact 49T-a of the timer 49T. NFB is tripped and resistor R is protected.

In this case, when prioritizing protection of the device, shorten the time limit of timer 49T according to the capacity of resistor R, and on the other hand, when prioritizing energization for important loads, excite the power breaker NFB's pulling coil SHT. By lengthening the time limit of the timer 49T so as to delay it, the protection characteristics can be easily changed according to the type of load in the same device.

Note that when the overcurrent relay 49 described above operates, the normally closed contact 49-a closes, so the alarm indicator lamp OL lights up.
It is possible to notify the occurrence of an abnormality in the current detector CR.

As described above, according to the current-limiting starting device according to the present invention, by using a normally closed type magnetic contactor, when the current detector fails, the overcurrent relay is activated to short-circuit the current-limiting resistor. Even when the magnetic contactor is abnormally excited, the current-limiting resistor remains in a short-circuited state, allowing continuous current to flow, and since no current flows through the resistor for a long time, there is no need to have extra resistance capacity, making the current-limiting resistor smaller. On the other hand, the resistor and the entire circuit can be protected by the contact configuration between the timer and the tripping coil of the breaker.

Furthermore, according to this study, even in the event of abnormalities such as loss of control circuit power, disconnection of control circuit wiring, no power supply to the electromagnetic switch coil due to disconnection, and non-operation due to failure of the electromagnetic switch, When the normally closed contacts of the current relay open, the contacts of the electromagnetic switch close, forming a short circuit of the current limiting resistor, and the load current is supplied through the contacts of the electromagnetic switch, so the load current is applied to the current limiting resistor. It does not flow, and the resistance not only heats up, but also burns out.
Fires can also be prevented.

[Brief explanation of the drawing]

The figure is a contact circuit diagram showing an embodiment of this invention. E...Power supply, L...Load, NFB...
...Power breaker, CT...Current transformer, CR
...Current detector, R...Current limiting resistor, 4
9... Overcurrent relay, 88... Magnetic contactor, 49T... Timer, SHT...
Breaker disconnection coil, OL... Alarm indicator lamp, CR-b, 8B-bl, 88-b 2.4
9-a, 49-b, 49 T-a... Contact.

Claims (1)

[Scope of utility model registration request] A series circuit formed by a current limiting resistor and an overcurrent relay, an electromagnetic contactor with a main contact installed in parallel to the series circuit, detects the load current, and operates after a predetermined time when the load current exceeds a set value. and a contact circuit that performs opening/closing control of the main contacts of the electromagnetic contactor, and closes the main contacts after a predetermined time when the current settles to a steady value after connection of the load based on the output of the current detector. In the current-limiting starting device that short-circuits the series circuit to supply power to the load, a normally closed type magnetic contactor is used as the short-circuit magnetic contactor, and an abnormality in the current detector, the contact circuit, or the magnetic contactor is detected. A current-limiting activation device characterized in that when a current-limiting activation device occurs, its main contact is closed to short-circuit the series circuit.