Find your nearest distributor
 Get in touch
 Log in

Safer & Faster Testing with DualGround™ Technology

 

Safer and Faster Testing with DualGround™ Technology

DualGround™ is Megger's groundbreaking technology that enables a safer and faster workflow because both sides of the circuit breaker remain grounded throughout the test.

Dynamic Capacitance Measurement
Megger test sets with DualGround™ technology uses Dynamic Capacitance Measurement (DCM) to measure contact timing on circuit breakers with both sides grounded. The results are identical to those achieved with conventional contact timing methods. This makes it possible to test circuit breakers without removing jumpers and bus-bar connections, opening up a wide range of applications in Gas Insulated Substation, Generator and Transformer breaker diagnostic testing.

Why is it safer?
Conventional timing requires at least one side of the circuit breaker to be ungrounded to allow the instrument to sense the change in contact status. Live high voltage conductors will induce currents in all parallel conductors due to capacitive coupling. In a disconnected circuit breaker with one side connected to earth and both disconnectors open, this current can reach double digit mA values which are lethal for humans.

How does it work?
The circuit breaker acts as variable capacitor when it operates. Its capacitance can be expressed as follows:



where:
C is capacitance
ε is the dielectric constant
A is the surface area of the breaker contacts
d is the distance between the surfaces of the contacts

When the circuit breaker moves from being open to closed, d decreases and as a result, C increases. However, once the circuit breaker is fully closed, C drops to 0.

The DCM technique uses high frequency to achieve resonance in the test circuit. The resonance frequency varies when the circuit breaker changes state, and this is how a change from open to closed (and vice versa) is detected. This also means that the technique is completely immune to the effects of 50 or 60 Hz interference.

Conventional vs DualGround™ Testing
The table below compares conventional testing procedure to the procedure on DualGround™ enabled instruments.
  Conventional DualGround™
Step
1
Site preparation (isolate work area, apply safety ground, issue permit to work). Site preparation (isolate work area, apply safety ground, issue permit to work).
Step
2
Connect test equipment. Issue sanction for test. Connect test equipment. Issue sanction for test.
Step
Authorized person removes ground. Risky step eliminated.
Step
Perform testing. Perform testing with both sides grounded.
Step
Authorized person removes ground. Risky step eliminated.
Step
6
Cancel sanction for test. Disconnect test equipment. Cancel sanction for test. Disconnect test equipment.
Step
Site closing (cancel permit to work, disconnect ground). Site closing (cancel permit to work, disconnect ground).
Using DCM we can obtain reliable measurements with both sides of the circuit breaker grounded, thus never exposing personnel to any induced currents.

 

Megger intruments related to this technical note:
Megger instruments with this technology will display the blue DualGround™ symbol.

TM1700
TM1800
MJOLNER Series
DLRO-H200

 

Back to news list

Filter By Product Category

Filter by date

I'm very happy with the device...brilliant build quality and just the right features for my application

Cyril Ryan

29th September #Southport Perry will be attending a Breakfast morning @YESSS_UK1 PR9 7RL. Join him for coffee and a… https://t.co/YN3C1c3b7u

22nd September #Bridgwater Tony will be attending a Calibration day at @cefonline TA6 4DB. All types of instrument… https://t.co/ynhqRA3srO

28th September #Sevenoaks Gordon will be holding a Calibration day at @cefonline TN14 5DS. Same day service and com… https://t.co/u8YlYGXXbp