How does a voltage transformer work?
A voltage transformer (VT, or Potential Transformer, PT) is a key device used in power systems to measure high voltage or provide protection signals. It converts high voltage into low voltage (usually 100V or lower) in proportion to the principle of electromagnetic induction, so that it can be safely connected to measuring instruments, relay protection devices or control systems. The following is description of its working principle:
1. Core working principle: electromagnetic induction
1) Basic structure
Primary winding: directly connected to the high-voltage line to be measured (such as 10kV, 35kV, etc.), with a large number of turns.
Secondary winding: outputs low voltage (such as 100V), with fewer turns, connected to measuring or protective equipment.
2) Working characteristics
Approximate open circuit operation: The impedance of the instrument or protection device connected to the secondary side is high, and the current is extremely small (milliampere level), so the voltage transformer is close to no-load state.
High-precision requirements: The error must be controlled within ±0.2%~±3% (according to the accuracy level) to ensure the accuracy of measurement and protection signals.
2. Key functions and features
1) Voltage isolation and safety
The insulation design isolates the primary high voltage and the secondary low voltage to prevent high voltage from being directly connected to the control room and ensure the safety of personnel and equipment.
2) Accuracy level
PT for measurement: 0.2 level (electric energy metering), 0.5 level (general measurement), with a small error range.
PT for protection: 3P level, 6P level, large errors are allowed but rapid response to faults is required (such as voltage drop during short circuit).
3) Load capacity
The secondary side load must be within the rated capacity range (such as 30VA). Overload will cause increased errors or even damage.
3. Typical application scenarios
1. Voltage measurement
Connect voltmeters, power meters, energy meters, etc.
2. Relay protection
Provide voltage signals for overvoltage/undervoltage protection, distance protection and other devices.
3. Synchronous control
Provide phase and voltage amplitude reference when connected to the grid for power generation.
4. Differences between voltage transformer and current transformer
Characteristics Voltage transformer (PT) Voltage transformer (PT)
Working state Approximately no-load (high impedance load) Approximately no-load (high impedance load)
Secondary side requirements No circuit break (will burn) No open circuit (generates dangerous high voltage)
Output signal Voltage (such as 100v) Current (such as 5A or 1A)
Ratio range 1000:1 to higher Usually fixed ratio (such as 1000:5)
5. Classification of voltage transformers can be divided into the following 3 categories according to the insulating medium
1) Dry voltage transformer
Insulating material: epoxy resin or casting material.
Features:
Maintenance-free, no risk of oil leakage, suitable for indoor dry environment.
2) Oil-immersed voltage transformer
Insulation material: transformer oil.
Features:
Strong insulation performance, good heat dissipation, suitable for outdoor or high humidity environment.
3) Gas insulated voltage transformer (GIS PT)
Insulation material: SF6 gas.
Features:
Highly integrated, small size, used for gas insulated switch cabinet (GIS).
Suitable for compact spaces such as urban substations.
6. Precautions
1) Regular verification: Ensure that the ratio and phase error meet the standards (such as once a year).
2) Insulation aging detection: The insulation performance of the core and winding needs to be checked after long-term operation.
Through the voltage transformer, the power system realizes the safe monitoring and control of high voltage, which is an indispensable "eye" for the stable operation of the power grid.
JDZX9-35 voltage transformer can be used to measure, monitor and relay the voltage of incoming and outgoing lines. It can accurately convert 35kV high voltage into low voltage, provide reliable voltage signals for various measuring instruments, protection devices and control systems in the substation, and ensure the safe and stable operation of the substation.
JDZX9-35 voltage transformer has many advatages:
Good insulation performance
The epoxy resin fully enclosed epoxy casting structure is adopted. This structure makes the transformer have high insulation strength, which can effectively prevent the internal circuit from contacting the external environment, and avoid the normal operation and measurement accuracy of the equipment affected by leakage, discharge and other problems. In addition, the insulation structure has good moisture and anti-fouling capabilities, can adapt to a variety of complex operating environments, and can still maintain stable performance in harsh climatic conditions and polluted environments.
High precision
For functions such as energy metering, voltage monitoring and relay protection, the accuracy of measurement is crucial. During the design and manufacturing process of JDZX9-35 voltage transformer, the material selection and processing technology of key components such as core and winding are strictly controlled, which can accurately convert high voltage into low voltage and provide reliable data support for the metering, monitoring and protection of power system.
Compact structure
small size and light weight: The overall structure is compact and has a mounting plate at the bottom, which is easy to install and fix. It can also be easily arranged in places with limited space such as substations and distribution rooms. Its light weight also facilitates operation during transportation and installation, reducing construction difficulty and labor costs.
