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Zhejiang ERG Technology Joint Stock Co.,Ltd

Mobile: 86-18257346462

Tel: 86-576-83200088


Contacts: Wu Nick/Bella Zheng/Blanca Chen

Add: 135 Haisha Road, Shaliu Economic DevelopmentZone, Sanmen County, Zhejiang, P.R.China

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Transformer Operating Voltage Regulations -Zhejiang ERG Technology Joint Stock Co.,Ltd.
- May 09, 2018 -

Transformer operating voltage regulations

-Zhejiang ERG Technology Joint Stock Co.,Ltd.

2.1 Range of operating voltage

The operating voltage should generally not exceed 105% of the rated voltage of the operating tap. For special use conditions, no more than 110% of rated voltage is allowed to operate.

2.2 The relationship between current and voltage

The relationship between current and voltage is as follows:

When the load current/rated current = K, (0≤K≤1), press u(%)=110-5K2

The operating voltage U is limited.

2.3 The effect of high voltage on transformers and hazards

When the power supply voltage rises, the magnetic flux Фm increases, so that the exciting current Im increases, the exciting current is a reactive current, and thus the reactive power increases, and the active power that the transformer allows passes decreases.

In addition, the voltage rises, the magnetic flux increases, the core is saturated and overexcitation occurs, and the voltage and magnetic flux waveforms of the transformer are distorted (formation of a peak wave), and the higher harmonic components are increased, thereby increasing the additional loss of the motor and the line and generating the system. The resonant overvoltage destroys the insulation of the electrical equipment while the higher harmonics interfere with the nearby communication lines.

For the transformer itself, because the voltage rise will over-excite the transformer, over-excitation of the transformer will inevitably cause overheating of the transformer core, make the core insulation aging, reduce the life of the transformer and even burn the transformer.

2.4 Causes of Overvoltage in Transformers

After the power system was disassembled due to accidents, the load rejection over-voltage, ferromagnetic resonance over-voltage, and the transformer tap position of some systems were improperly adjusted. At the end of the long line, no-load transformers or other operations were performed, and the generator frequency was less than the rated value. Early excitation current, generator self-excitation and other conditions.

2.5 Voltage Adjustment of Transformer

Transformer operating voltage adjustment is achieved through the tap switch, transformer tap switch settings, divided into two kinds of non-excitation voltage regulator and on-load voltage regulator switch.

The non-excitation voltage regulator switch must be under the conditions of power outage to tap and shift. When shifting the single-phase switch, pay attention to the three-phase shift gear to be consistent. After the gear shift, the transformer ratio test must be done to confirm the three-phase gear. The power can be transmitted only when they are in agreement.

The on-load tap-changer can be tapped and adjusted under live conditions. When shifting, the following regulations should be observed: The tap changer, voltage, and current should be monitored when voltage is adjusted step by step.

The phase-to-phase switch of a three-phase transformer or the on-load tap-changer of a single-phase transformer group should be operated in three-phase synchronous operation.

When the on-load tap-changer is operated in parallel, its voltage regulation operation should be synchronized and synchronized in stages.

When the on-load tap-changer and the non-exciter tap-changer are operated in parallel, the tap voltage of the two transformers should be as close as possible.

2.6 Transformer Capacity at Voltage Adjustment

When the voltage is adjusted, the capacity of the transformer is as follows:

No excitation voltage regulation within ±5% conversion tapping, transformer capacity constant; large load voltage range, such as ± 7.5% and ± 10% tap range, at the maximum negative tap, that is at -7.5 When the % and -10% taps are made, the transformer capacity should be reduced due to the limitation of the wire current, and if the manufacturer does not specify it, it is usually reduced by 2.5% and 5%.

Thank you for your kindly attention. Hope everything goes well with you.

This is Blanca Chen, from Zhejiang ERG Technology Joint Stock Co.,Ltd. We manufacturer and design transformers accessories. 


Products: (Sorry that for the e-mail not to be sent back, our catalogue and web are not attached for our first contact.)
All kinds of transformer cooler
Oil pump
Butterfly valve
Oil flow relay 
Control cabinet

6. Terminal box etc.
ERG join the draft of the standard for chinese government in transformers accessories, with certifications:CE, CRCC,IRIS,EUP,TS,CNAS,BV etc. 



Whatsapp/Wechat/Tel: 86 13626615457



Best Regards,

Blanca Chen