Discharge Sticks

A discharge stick is used to release, in a controlled way, the electrical charge that remains in cables, capacitors and test set-ups after they have been disconnected. Long MV cables and capacitor banks can hold a dangerous charge for some time after disconnection; contact before this charge is released can cause serious accidents. Cable testing teams, power factor correction maintenance staff, test laboratories and substation operators are the main users.

Which model?

Model	Operating voltage	Typical use
HRD-27	Discharge voltage up to DC 27 kV	Built-in 600 kΩ resistor; controlled discharge of cables and capacitors
HRD-27S	Discharge voltage up to DC 27 kV	Discharge monitored by audible and visual indicator; 2 interchangeable tips
Simple discharge stick	AC 6.6 kV	Made-to-order type without built-in resistor

In the HRD-27, discharge takes place through a built-in resistor: with a 1 µF load, the voltage falls from DC 27 kV to below 50 V in 5 seconds or less; the stick's capacitance limit is 1 µF. What sets the HRD-27S apart is the indicator in the middle of the body; the operator follows the progress of the discharge visually and audibly instead of relying on time alone. The simple type has no built-in resistor and is made to order.

Points to note in use

• A discharge stick is used only on circuits that have been disconnected and isolated; the absence of voltage must first be verified with a suitable voltage detector.
• The stick's earth connection must be made before the discharge tip touches the equipment.
• Discharging does not replace permanent earthing; after the charge has been released, the circuit must be kept earthed with an earthing set for the duration of the work.
• Do not use the stick in applications exceeding its maximum discharge voltage.

For earthing sets see earthing equipment; for the causes of residual charge see our article What Is a Discharge Stick?.

Frequently Asked Questions

Which model should be preferred after cable testing?

When discharging a cable after DC withstand tests, the HRD-27, with a defined discharge time and capacitance limit, or the HRD-27S, which signals completion of the discharge with an indicator, is suitable. The test voltage must not exceed DC 27 kV.