A transformer is essentially a special type of transformer. Its core purpose is not to transmit the electrical energy, but to "transmit information" - to convert high voltage and high current into safe, standardized low voltage and low current in precise proportions for measurement, protection, and control.
You can understand it as the "scout" and "safety isolator" of the power system.
Transformers are mainly divided into two categories, with clear division of work:
|
type |
voltage transformer |
current transformer |
|
English/Abbreviation |
Potential Transformer (PT) 或 Voltage Transformer (VT) |
Current Transformer (CT) |
|
core mission |
Transform voltage |
Transform current |
|
working principle |
Working in a state close to no-load, converting high voltage (such as 10kV) proportionally to standard low voltage (usually 100V or 100/√ 3 V) |
Working in a state close to short circuit, convert high current (such as 1000A) proportionally to standard low current (usually 5A or 1A). |
|
connection method |
Parallel connection between high voltage lines and ground in a primary system. |
Parallel connection in the high voltage line of a primary system and series connection in the high current line of a primary system. The secondary side of the key characteristic must be reliably grounded to prevent high voltage from entering the low voltage side and ensure safety. During operation, the secondary side must not be open circuited! Otherwise, it will generate extremely high voltage, endangering equipment and personal safety. between. |
|
Key Features |
The secondary side must be reliably grounded to prevent high voltage from entering the low voltage side and ensure safety. |
During operation, the secondary side must not be open circuited! Otherwise, it will generate extremely high voltage, endangering equipment and personal safety. |
|
Image metaphor |
A high-precision, fixed ratio 'voltage divider' |
A high-precision, fixed ratio 'splitter' |
Why the power system can't work without transformers?
The existence of transformers mainly solves three major problems:
1. Safety Isolation
·Problem: The voltage in the power system can reach thousands to hundreds of thousands of volts, and the current can reach tens of thousands of amperes, making it impossible to measure directly with ordinary instruments and extremely dangerous for operators.
·Solution: The transformer establishes electrical isolation between the primary side (high voltage side) and the secondary side (low voltage side). The staff operates on the secondary side (low voltage, low current), completely isolated from the high voltage environment, greatly ensuring safety.
2. Standardization&Miniaturization of Instruments
·Problem: If specialized instruments are manufactured for each voltage and current level, the cost is extremely high and unrealistic.
·Solution: Regardless of the voltage/current on the primary side, the secondary side outputs a unified standard value (such as 100V voltage, 5A current) after transformation through a transformer. Therefore, all measuring instruments and protective devices can be designed and manufactured according to these standard values, achieving universality, miniaturization, and economy.
3. Implement Centralized Control&Protection
·Problem: Real time monitoring of the entire power grid is required, and it should be quickly cut off in case of faults.
·Solution: Numerous transformers from different locations can remotely transmit the voltage and current signals of the system to the instruments and relay protection devices in the central control room, achieving centralized monitoring. When a short circuit or other fault occurs in the system, the protection device can quickly act based on the signal transmitted by the transformer to cut off the faulty circuit.
Core application scenarios
1. Measurement&Metering
·Provide input signals for voltmeters, ammeters, power meters, and energy meters (kWh meters). Inside your home or factory's electricity meter, there are current transformers and voltage transformers connected.
2. Relay Protection
·This is one of the most important functions of a transformer. The protective relay analyzes the current and voltage signals transmitted by the transformer in real time to determine whether there is a short circuit, overload or other fault in the power grid, and immediately issues a trip command.
3. System Control&Monitoring
·Providing real-time data for the dispatch automation system and fault recording devices of the power grid is the "sensory nerve" of the smart grid.