Reactor Switching Voltage Drop Calculator

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What is Reactor Switching?

Shunt reactor switching is an unique and challenging work for circuit breakers.

It involves a complex interaction across the characteristics of the circuit breaker, such as its type, whether it is gas (or) vacuum, and its current chopping capability, arc voltage, and arcing time, and the characteristics of the reactor load circuit, which are expressed by its inductance, effective capacitance, and reactor grounding arrangement.

Voltage Drop in Reactor Switching

A “reactor switching voltage drop” is a sudden decrease in voltage that occurs when a shunt reactor is switched on in an electrical power system.

This drop in voltage is induced by the large current generated by reactor during the initial switching moment, which results in a voltage drop across the impedance of the system.

In simple terms, the reactor acts like a heavy load for a brief period of time when it is switched on, which causes a voltage drop.

Reactor Switching Voltage Drop Calculation

Base Selection

The base selection is essential for doing per-unit system computations, which facilitate electrical power system analysis.

The basic values are:

Base Voltage (kV): The system voltage level used for computations.

Base MVA (MVA): The base MVA (MVA) is the system’s power rating.

Base Current (A): Base Current (A) is calculated using the following formula:

I_base = (Base MVA X 1000)/(√3 X Base KVA)

Base Impedance (Ω): Base impedance (Ω) is calculated using the formula:

Z_base = (Base KV²)/(Base MVA)

Reactor Details

The reactor specifications consist of the following:

Rating of the Reactor (MVAr): The reactor’s rating (MVAr) is its reactive power.

Voltage Level (kV):  Voltage Level (kV) is the nominal voltage that is utilized when the reactor operates.

Reactor Impedance (Ω): The reactor’s overall impedance for current flow.

Per-Unit Voltage: Per-Unit Voltage is the ratio of working voltage to the base voltage.

Per-Unit Impedance: Per-Unit Impedance is the reactor’s impedance converted to per-unit value utilizing base impedance.

Z_{reactor pu} = Z_reactor/ Z_base

Source Details

The electrical source parameters should be considered while calculating the reactor switching voltage drop.

The primary parameters are:

Source Voltage (kV): The source voltage (kV) is the actual system voltage prior to switching.

Fault Current (kA): The maximum short-circuit fault current at source.

Fault MVA: Fault MVA is the power available at source, calculated utilizing:

S_Fault = √3 X Source Voltage X Fault Current

Per-Unit Voltage: The source voltage is expressed in per-unit form.

Source Impedance (Ω): The source impedance (Ω) represents the equivalent impedance of power source.

The source impedance per unit is calculated as follows:

Z_{source pu} = Z_source/ Z_base

Thevenin Voltage Calculation

The equivalent voltage & impedance of Thevenin are calculated in order to calculate the voltage drop following reactor switching:

Thevenin Voltage in Per-Unit:  The effective voltage at the switching point is known as the Thevenin Voltage in Per-Unit.

Thevenin Impedance in Per-Unit: The combined impedance of the source & reactor in a per-unit is known as the “Thevenin Impedance.”

Thevenin Impedance in Per-Unit: The percentage decrease in voltage carried on by reactor switching is known as the “percentage voltage drop” (%).

% Voltage Drop = (Voltage Drop/Source Voltage) X 100

Voltage Drop per Unit: The reduction in system voltage caused by reactor impedance.

Voltage Drop in kV: The true voltage drop in kV.

Final Voltage in kV: The system voltage after reactor is turned on.

Summary

Assessment of system voltage stability during transient occurrences requires reactor switching voltage drop calculation. Engineers can prevent voltage drops that could impact connected loads by studying Thevenin’s equivalent voltage, impedance, & percentage voltage drop. Reactors regulate voltage and stabilize high-voltage transmission lines, making this analysis essential.

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