Abnormal Voltage Issue on LV side in STS-(3000K,6000K)-H1 Smart Transformer Station

Inspection

Check the voltage displayed on the Voltmeter and SmartLogger.

1. If the voltage displayed on the voltmeter is normal but that displayed on the SmartLogger is abnormal, the fault is located on the measurement device side of the STS.

Set the multimeter to the AC voltage range, and measure the voltages to the ground of the terminal blocks X6:1, X6:2, and X6:3 on the rear of the measurement device, in normal cases, the X6:1 voltage to the ground is 100 V, the X6:2 voltage to the ground is 0 V, and the X6:3 voltage to the ground is 100 V. Check the cable connection of the terminal. There is a high probability that the cable connection is loose.

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Pic 2

If the measured voltage is normal and the terminal is not loose, the fault is caused by an internal fault of the measurement device.

Please, take pictures of the measurements and contact the service team for the replacement of the faulty device. Besides the pictures of the measurements, you need to provide the picture of the measurement device's SN and the SN of the STS. In case the warranty for STS is still valid, Huawei will provide the new device.

You can replace a new measurement device.

Replace the measurement device after the transformer station is powered off at night.

Before replacing the measurement device, you can take a picture, and after replace, double-check the cable by the picture.

2. If the voltage displayed on the voltmeter is abnormal but the voltage displayed on the SmartLogger is normal, the fault is caused by the voltmeter.

Set the multimeter to the AC voltage range and measure the voltage of the wiring terminal of the voltmeter to the ground. In normal cases, the voltage of phase A to the ground is 100 V, the voltage of phase B to the ground is 0 V, and the voltage of phase C to the ground is 100 V.

Check the voltage of the power supply. In normal cases, the voltage is 220 V. Check the cable connection of the terminal. The cable connection may be loose.

Pic 3

If the measured voltage is normal and the terminal is not loose, the fault is caused by an internal fault of the voltmeter. Replace the voltmeter.

Please, take pictures of the measurements and contact the service team for the replacement of the faulty device. Besides the pictures of the measurements, you need to provide the picture of the voltmeter's SN and the SN of the STS. In case the warranty for STS is still valid, Huawei will provide the new device.

Before replacing the voltmeter, power off the voltmeter, switch off the circuit breaker 1FB5 on the low-voltage side of the voltage transformer and disconnect the power supply 1FB2 of the voltmeter.

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Take photos of the cable connections before the replacement and compare the photos with the cable connections after the replacement.

3. If the voltages displayed on the voltmeter and SmartLogger are the same, that is, both are abnormal or 0, the fault is located on the VT side. Strictly follow the following steps to perform the check

3.1 Switch off the MCB 1FB5.

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3.2 Turn on the VT fuse switch 3FA and take out the internal fuses. Use a multimeter to measure the resistance of the three fuses. In normal cases, the resistance is close to 0. If the fuse is damaged, the resistance is infinite. If a fuse is damaged, do not replace the fuse and do not switch on the circuit breaker.

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Pic 7

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3.3 Use a multimeter to measure the resistance between phases A and B, phases B and C, and phases A and C on the upper side of the MCB 1FB5 (Pic 5). In normal cases, the resistance is about 1Ω. If the resistance is larger, the VT may be open-circuited.

3.4 Measure the resistance between phases A and B, phase B and C, and phase A and C at the bottom of the MCB. In normal cases, the resistance should be greater than 1KΩ. Measure the resistance between phase A, phase B, phase C, and the ground. In normal cases, the resistance should be greater than KΩ. If the resistance is smaller, a short circuit may occur on the measurement and control device or meter, rectify the short circuit fault. For details, see chapter 4.

3.5 Use a multimeter to measure the resistance between phases A and B and the resistance between phases B and C at the lower part of the knife fuse switch. The normal resistance is about 60Ω. If the resistance is close to 0Ω or is at the kΩ level, the VT is short-circuited or open-circuited.

3.6 Replace the VT if the measurement results in sections 3.3 and 3.5 are abnormal. Replace the VT only when the transformer is powered off. For details, see chapter 5.

Please, take pictures of the measurements and contact the service team for the replacement of the faulty device. Besides the pictures of the measurements, you need to provide the picture of the VT's SN and the SN of the STS. In case the warranty for STS is still valid, Huawei will provide the new device.

4. Method of Checking the Abnormal Resistor of the MCB 1FB5

Switch off MCB 1FB5 (Pic 5) and measure the resistance between phases A, B, and C at the bottom of the MCB. In normal cases, the resistance is greater than KΩ. If a short circuit occurs in the loop, the resistance may be less than 100Ω. Measure the resistance between the lower parts A, B, and C of the MCB and the ground. In normal cases, the resistance is at the MΩ level. If a short circuit occurs in the loop to the ground, the resistance may be less than 1 kΩ. If the resistance is too small, disconnect the X6:1, X6:2, and X6:3 (Pic 2) cables from the terminal block on the rear of the measurement and control device to determine whether the fault is caused by the measurement and control device. After the cables are disconnected, measure the resistance of the terminal and the cable connection. If the resistance of the terminal is too small, the fault occurs in the measurement and control device. If the resistance of the cable is too small, disconnect the wiring terminal at the back of the voltmeter (Pic 3) to determine whether the fault is caused by the voltmeter. After the voltmeter is disconnected, measure the resistance of the terminal and the wiring terminal. If the resistance of the terminal is too small, the fault is caused by the voltmeter, if the resistance of the cable is low, the cable is faulty.

If the fault is caused by measurement and control, replace a new one see chapter 1. If the fault is caused by the voltmeter, replace the voltmeter see chapter 2. If the fault is caused by the cable, the cable is damaged. Check the cable at the bending position and check the cable integrity. If the cable is damaged, use insulation tape to repair the cable. After the repair, wrap the cable again to ensure that the cable is far away from the position where it is easy to cut.

5. Procedure for replacing the voltage transformer:

5.1 Turn off the fuse switch on the 800V side of the voltage transformer in the low-voltage cabinet, take out the internal fuses (Pic 7), and use the resistance scale of a multimeter to measure the resistance of the fuses (Pic 8). In normal cases, the resistances of the three fuses are small and close to each other. The resistance of a fuse that has been blown is infinite. Replace a fuse that has been blown. After the fuse is measured, reinstall the fuse switch. The fuse switch remains OFF.

5.2 Take photos of the faulty voltage transformer, especially the cable connection position. Remove the voltage transformer.

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5.3 Check the cable connection. Use a multimeter to measure the resistance between the two wires on the 800 V side of the voltage transformer. In normal cases, the resistance is infinite. Measure the resistance between the two wires on the 100V side of the voltage transformer. In normal cases, the resistance is greater than 1KΩ.

5.4 Install a new voltage transformer and connect cables according to the original photos.

5.5 Closing the fuse switch