The transformer needs voltage regulation mainly because the fluctuation of the grid voltage and the load change will lead to the instability of the secondary voltage, thus affecting the normal operation of the electrical equipment, the purpose of voltage regulation is to stabilize the output voltage.
• The effect of voltage fluctuations
• The voltage in the grid is not constant and will fluctuate due to a variety of factors (such as the length of the supply line, changes in the supply voltage, etc.). This fluctuation will cause the voltage of the secondary side of the transformer to change, if the voltage is high or low, it may cause damage to the electrical equipment or make it unable to work normally.
• Impact of load changes
• Different load sizes and power factors connected to the secondary side of the transformer will also cause changes in the secondary voltage. For example, if the load in a certain area suddenly increases, and the output voltage of the transformer is not adjusted accordingly, the voltage in the area may drop, affecting the normal operation of the equipment.
Pressure range
Definition
• Voltage regulation range refers to the difference between the maximum and minimum voltage values that a transformer can adjust based on its rated voltage, usually expressed as a percentage. By changing the position of the tap-changer, the transformer can adjust the voltage within the set voltage regulation range to meet the needs of the power system or load.
Expression Mode
• Percentage representation
The voltage range is usually expressed as a percentage of the rated voltage. For example, a voltage regulation range of ±2*2.5% means that the voltage of the transformer can be increased or decreased by 5% from its rated voltage,
• Number of taps
Different positions on the tap-changer correspond to different voltages, and each position is called a Tap. The range of voltage regulation is determined by the location of these taps.
• Specific voltage value
The voltage range can also be expressed by a specific voltage value. For example, a transformer with a rated voltage of 110kV can be adjusted between 99kV and 121kV if the voltage regulation range is ±10%.
Principal tap
9th gear 132KV
Max tap
132* (1+8*1.25%) =145.2KV
Maximum negative gear (Min tap)
132 * (1-8 * 1.25%) = 118.8 KV
Sum up
The step size of each gear (tap) is 2.5%, with the rated gear (9th gear) as the initial gear, to positive 8 gear, 2.5% per gear, to negative 8 gear, 2.5% per gear, a total of 17 gear, the overall voltage regulation range of ±10%, written as ±8*1.25%
Voltage regulator switch
No-Load Voltage Regulation (NLTC)
Definition
To be suitable for adjusting tap-changer when the transformer is not live. This voltage regulation method needs to be carried out when both the primary and secondary sides of the transformer are disconnected from the grid
English name
No-load tap changer (NLTC)
Off-circuit tap changer (OCTC)
De-energized tap changer (DETC)
Voltage regulation range
The general no-load voltage regulation is ±2*2.5%, 5 levels
On Load tap changer (OLTC)
Definition
On-load voltage regulation is a voltage regulation method that can change the voltage by changing the tap gear when the transformer is running under load.
English name:
On-load tap changer (OLTC)
Load tap changer (LTC)
Voltage regulation range
The range is relatively large, such as ±8*1.25%, 17 gear pressure adjustment, or larger, such as 21 gear
Components of on-load switch
Switch body
• Located inside the tank, connected winding for pressure regulation
Type
Oil immersed switch (Oil type)
•Oil-immersed on-load regulator uses transformer oil as insulation and arc extinguishing medium. When the switch switches the tap, the oil is extinguished by physical and chemical processes.
• Cheap price, domestic about 6W, such as Shanghai Huaming, imported may be 5-6 times the price, such as Germany MR, Sweden ABB and so on
Vacuum switch (Vacuum type)
• Vacuum on-load voltage regulator uses a vacuum interrupter. When switching taps, the arc is extinguished quickly in a vacuum environment.
• High price, domestic about 21W, such as Shanghai Huaming, imported may be 5-6 times the price, such as Germany MR, Sweden ABB and so on
Motor Drive Unit
• It is responsible for driving the switch to complete the switching of the tap. The electric mechanism is composed of motors, gear drives, control systems, etc., to achieve local control and remote control.
• Motor voltage: common 400VAC, may also be other, according to customer requirements
AVR(Automatic Voltage Regulator)
The AVR detects the difference between the output voltage and the set value and automatically adjusts the excitation current or tap position to maintain the stability of the output voltage.
Remote transformer control cabinet (RTCC)
Remote monitoring of transformer pressure, temperature, gas relays and other signals as well as voltage regulation
