Reactive Power and Capacitor Bank Controller Testing

A reactive power controller decides when to switch capacitor steps from two measurements: voltage and current, and the phase angle between them. The output is a set of relay commands to contactors. Testing the controller means reproducing the voltage, current and phase angle that make it compute a target power factor, then reading the commands and their timing. It is a secondary-injection test with a phase angle at its centre.

What the controller computes

Input or output	What it represents	How the test set connects
Voltage input	Bus voltage, usually through a VT	One or three voltage channels at the VT secondary value
Current input	Load current, usually through a CT	One or three current channels at the CT secondary value
Phase angle	Displacement between V and I; the controller derives active and reactive power from it	Independent phase control between the voltage and current channels
Step outputs	Contactor commands for capacitor steps	Binary inputs record which step switches and when
Alarm and inhibit	Overvoltage, harmonic, maintenance	Binary inputs record the alarm state

What to prove

Function	Injection	Pass criterion
Power factor or kvar threshold	V/I at a known phase angle, swept across the target	The correct step switches at the set threshold, not before
Switching delay	Threshold held for a defined time	Output after the set delay; no output on a shorter excursion
Step rotation and equalisation	Repeated threshold crossings	Steps rotate or the least-used step is selected, as configured
Overvoltage and undervoltage	Voltage ramp beyond the limits	All steps disconnect or reconnect at the set voltage with the set delay
Harmonic blocking	Fundamental V/I plus 5th or 7th harmonic	Switching blocked or inhibited when the harmonic content exceeds the setting
Manual and remote inhibit	Digital input or command	No switching; alarm state correct
Discharge and reconnection delay	Step-off command, then a new demand	Reconnection held for the set discharge time

Reproducing a power factor

The controller does not see a power factor; it sees a voltage phasor, a current phasor and the angle between them. To command a 0.95 lagging power factor at rated voltage and current, set the voltage at the VT secondary value, set the current at the CT secondary value, and set the current phasor 18.2 degrees behind the voltage. To cross the threshold, move the angle in small steps and watch the step output. The test set’s phase accuracy (0.1 degrees on the VAE-660, 0.2 degrees on the VAE-430) is the limit on how finely the threshold can be located.

Harmonic blocking

Capacitor bank controllers block switching when the harmonic distortion exceeds a threshold, because switching into a resonant condition can amplify the harmonic. The test set can superpose harmonics 1–20 in PC mode (1–6 in local mode on the VAE-430; 2–20 on the VAE-660). Inject the fundamental at the rated point, then add the 5th or 7th harmonic in steps until the controller blocks. Record the threshold and confirm that the block clears when the harmonic is removed.

What the test set does not do

Item	Why
Capacitor bank main circuit	The test set injects into the controller, not into the power circuit
Inrush current and discharge	Requires the real bank, contactors and a transient recorder
Contactor and fuse health	Mechanical and thermal checks are outside the injection scope
Power quality compliance	No flicker, interharmonics or Class A measurement; use a power quality analyser
Capacitance measurement	Requires a capacitance bridge or a dedicated tester

Frequently asked questions

Can the VAE-430 test a reactive power controller?

Yes. A single-phase voltage and current with adjustable phase angle is enough for most controllers. Three-phase controllers use the same principle with three voltage and three current channels.

How accurate is the phase angle?

0.2 degrees on the VAE-430 and 0.1 degrees on the VAE-660. For a threshold test that is enough to locate the switching point well inside the controller’s own repeatability.

Can it test the harmonic blocking function?

Yes, within the harmonic range: 1–20 in PC mode on the VAE-430, 2–20 on the VAE-660. It cannot reproduce flicker, interharmonics or high-frequency distortion.

Does it test the capacitor steps themselves?

No. It tests the controller outputs. The steps, contactors, fuses and discharge resistors are tested with the power circuit and a dedicated procedure.

Can it verify the controller’s own measurement accuracy?

It can compare the controller’s displayed values with the injected values. That is a functional check, not a calibration; the test set is a 0.1 % AC working source, not a metrology standard.