Earthing Transformer
Three-phase neutral earthing transformer with winding connection according to Zigzag scheme.
Description
Unit Earthing Transformer is a three-phase neutral earthing transformer with winding connection according to Zigzag scheme. This unit allows the creation of an artificial neutral in an ungrounded three-phase power supply system. The artificial neutral creates a low impedance path for zero sequence current and a high impedance path for direct sequence current. The common point allows a Delta voltage source to be used to connect a single-phase load.
For more information on the operating modes of a three-phase Delta system, see Problem solving for delta connection of transformer windings.
Equations
This block is implemented in both the electrical and magnetic domains, representing the physics of phase windings and magnetic core. The equivalent block diagram includes the blocks Reluctance, Winding and Eddy Current.
When the windings are zigzag connected, phases a, b and c represent each rod of the magnetic core.
The relationship between electrical and magnetic properties can be obtained by applying a few mathematical steps based on the rule of conservation of magnetic flux and Ohm’s law for a magnetic circuit.
For grounding transformers, the connections between phases and all windings are the same.
In the following equations:
-
- number of winding turns.
-
- magnetising resistance between phases.
-
- leakage resistance of the primary winding.
-
- conductivity of the eddy current loop between phases.
Then the relationship between the inductance matrix in the electrical domain and the inductance matrix in the magnetic domain can be written as:
The diagonal elements are the sum of the scattering inductance and magnetising inductance for each phase, so that:
Hence:
Parameters
Main
Rated apparent power - rated apparent power
`100e6 V*A (by default)
The rated power passing through the transformer. The value must be greater than 0.
Rated voltage - RMS line voltage
24e3 V (by default).
Nominal RMS line voltage.
The value must be greater than 0.
Rated electrical frequency - rated electrical frequency
50 Hz (By default).
The nominal or nominal frequency of the AC mains to which the transformer is connected. The value must be greater than 0.
Units - system of units
pu (by default) | SI.
Unit system for impedance parameterization.
Dependencies
The usage of other parameters depends on the value of this parameter.
Zero-sequence resistance, pu - zero-sequence resistance
0.01 (by default) | `positive scalar'.
Zero-sequence resistance in O.E.
The value must be greater than 0.
Dependencies
To use this parameter, set the Units parameter to Per unit.
Zero-sequence reactance, pu - zero-sequence reactance
0.3 (by default) | positive scalar
Zero-sequence reactance in O.E. The value must be greater than or equal to the magnetic flux losses of the primary winding.
Dependencies
To use this parameter, set the Units parameter to Per unit.
Shunt magnetising resistance, pu - core magnetising resistance
500 (By default) | positive scalar
Core magnetising resistance in O.E. The value must be greater than 0.
Dependencies
To use this parameter, set the Units parameter to Per unit.
Shunt magnetizing reactance, pu is the magnetic inductance of the transformer core
500 (By default) | positive scalar
Magnetic inductance of the transformer core when operating in its linear region in O.E. The value should be greater than 0.
Dependencies
To use this parameter, set the Units parameter to Per unit.
Zero-sequence resistance - zero-sequence resistance
`0.0576 ohms (by default).
Zero-sequence resistance. The value must be greater than 0.
Dependencies
To use this parameter, set the Units parameter to SI.
Zero-sequence inductance - zero-sequence inductance
`1.728 Gn (by default).
Zero-sequence inductance. The value must be greater than 0.
Dependencies
To use this parameter, set the Units parameter to SI.
Shunt magnetising resistance - core magnetizing resistance
2880 ohms (by default) | `positive scalar'.
Core magnetising resistance . The value must be greater than 0.
Dependencies
To use this parameter, set the Units parameter to SI.
Shunt magnetising inductance is the magnetic inductance of the transformer core
2880 Gn (by default) | `positive scalar'.
Magnetic inductance of the transformer core when operating in its linear region. The value must be greater than 0.
Dependencies
To use this parameter, set the Units parameter to SI.