What Could Be Causing Negative Reactive Power in a Three Phase Power System?

In summary, in a three phase power system with delta connected 66kV transmission line, one line/phase has negative (capacitive) reactive power while the other two lines/phases have positive reactive power. This could be caused by various factors and can be mitigated by adding capacitors or inductors, or by using a synchronous condenser. A synchronous condenser is a device that adjusts conditions on the electric power transmission grid by generating or absorbing reactive power. To determine the cause of this negative reactive power, it is important to check the accuracy of the instruments and the direction of power flow in that leg. A complete vector diagram of the readings can also provide more information.
  • #1
Nick Kuza
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In a three phase power system,delta connected 66kV transmission line,the reactive power in one of the line/phase is negative(capacitive) while the reactive power in the other two lines/phases is positive.What is causing the reactive power to be negative(capacitive) in this phase?What are some possible solutions towards mitigating this negative(capacitive) reactive power?
 
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  • #2
Welcome to Physics Forums.

Adding capacitors will decrease the Vars, adding inductors will increase the Vars, or you can use the what's called a Synchronous Condenser which will either increase or decrease Vars.

In electrical engineering, a synchronous condenser (sometimes called a synchronous capacitor or synchronous compensator) is a device identical to a synchronous motor, whose shaft is not connected to anything but spins freely.[1] Its purpose is not to convert electric power to mechanical power or vice versa, but to adjust conditions on the electric power transmission grid. Its field is controlled by a voltage regulator to either generate or absorb reactive power as needed to adjust the grid's voltage, or to improve power factor.
 
  • #3
This could be caused by many things - How much are you talking about? How many VAR relative to Watts, if it is a small amount(near unity - or very low real power flowing) this could be a "normal" system condition, one line is actually more capacitive than the other lines. However is it is a significant amount of VARs at significant power - I would check that the CTs/PTs , instruments are connected properly. Is the POWER in that leg reversed as well?
What device is being used to tell you that the PF is +/-? Is there any way to get a complete vector diagram of the readings.
 

1. What is negative reactive power?

Negative reactive power is a type of power that is consumed and stored by inductive components in an electrical system. It is commonly referred to as "lagging" power, as it lags behind the voltage in a circuit.

2. How is negative reactive power different from positive reactive power?

Negative reactive power is the opposite of positive reactive power, which is generated and stored by capacitive components in an electrical system. Positive reactive power is commonly referred to as "leading" power.

3. What causes the presence of negative reactive power in a circuit?

Negative reactive power is caused by inductive loads, such as motors or transformers, that require a magnetic field to operate. This magnetic field stores energy and creates the lag between voltage and current in a circuit.

4. Why is negative reactive power considered undesirable?

Negative reactive power can cause inefficiency in an electrical system, as it requires additional energy to be supplied to maintain the voltage levels. This can lead to increased energy costs and can also result in power quality issues.

5. How can negative reactive power be managed or reduced?

Negative reactive power can be managed or reduced through the use of power factor correction devices, such as capacitors, which can supply the reactive power needed by inductive loads. This can improve the overall efficiency and power quality of an electrical system.

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