JPS6012853B2 - Motor overload protection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an overload protection device for an electric motor.

Conventionally, a motor overload protection device generally detects the load current of the motor using a CT (current transformer) or the like, and protects the motor using a bimetal type or induction disk type overload relay. However, the following problems arise with conventional overload relays in motors for primary cooling pile pumps in pressurized water nuclear power plants. This is because the difference between the fluid temperature when the pump is started and the fluid temperature during normal operation is very large, and this results in a difference in the density of the fluid and, ultimately, in the motor current. The following table is an example.

Normally, overload relays are set to about 115% of the normal current, but as shown in the table above, if they are set to match the overload condition, they will not be able to provide protection in the event of an overflow, and if they are set to match the overload condition, as shown in the table above, If set, the protection relay will operate even though it is normal when it is cold.

If the motor rating is continuous based on the cold state, there is no problem from the perspective of protecting only the motor by setting the protection relay based on the cold state, but if the pump This cannot be said to be sufficient in terms of abnormality monitoring of the entire system, including the system.

Furthermore, the rating of ordinary electric motors is continuous in hot conditions due to economic efficiency.
Considering the short time in the cold state, it can be said that this is insufficient. The present invention has been made to eliminate these drawbacks, and is designed to automatically correct the set value of the overload protection relay depending on the temperature of the pump fluid.

FIG. 1, which is an embodiment of the present invention, will be explained below. In Fig. 1, 1 is a pump, 2 is a pipe through which fluid passes, and 3 is a pump.
4 is the neck temperature device that detects the temperature of the fluid, and 4 is the pump 1.
5 is a current transformer that detects the load current of the motor, 6 is a secondary current proportional to the load current obtained by the current transformer, and is compared with a set value to determine whether the set value has been exceeded. This is an overload protection device that is activated at certain times and performs operations such as tripping the shield breaker 7 and issuing an alarm. As shown in the figure, the temperature of the fluid is detected by the side temperature device 3, and the set value of the overload protection device 6 is automatically changed based on the signal, so that the motor and pump are always adapted to the condition of the fluid. Appropriate protection of the entire system can be achieved. Of course, in this case, it goes without saying that the relationship of fluid temperature→fluid density→motor output→motor current is known in advance, and appropriate correction is made in the overload protection device 6 according to the fluid temperature.

FIG. 2 is an explanatory diagram thereof, in which 8 is a curve showing the relationship between the setting value and operating time of the overload protection device 6 in the overflow state, and 9 is the setting curve for the overload state.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, 1 is a pump, 2 is a pipe, 3 is a side heating system, and 4 is a pump.
is an electric motor, 5 is a current transformer, 6 is an overload protection device, and 7 is a breaker. FIG. 2 shows setting curves for the overload protection device according to the present invention, where 8 is a curve for a warm state and 9 is a curve for a closed state. Figure 1 Figure 2

Claims (1)

[Claims] 1 In devices that detect the current of the electric motor that drives the pump and are equipped with an overload relay that operates when the detected current exceeds a set value to protect the electric motor from overload, the temperature of the fluid discharged from the pump is Equipped with a temperature measuring device to detect
A signal from the temperature measuring device is used to lower the set value when the fluid temperature becomes high, and to increase the set value when the fluid temperature becomes low. Electric motor overload protection device.