Energy Measurement Flashcards
1
Q
What are the three most common single phase meter sockets designed for
A
- 120/240V three wire service
- 120V single phase service
- 120/208V three wire network service
2
Q
Describe a 120/240V three wire service
A
- The most common meter socket for single phase circuits
- Can be designed for overhead or underground services
- 4 jaws
3
Q
Describe a 120V single phase service
A
- Only one 120V circuit is required
- 4 jaws
4
Q
Describe a single phase, three wire 120/208V service
A
- Single phased panel boards are used on this system
- Has 2 phase conductors and a common conductor
- Five jaws
- Contains a tickler
5
Q
What is a tickler?
A
- It maintains the correct voltage drop and the correct phase relationship with the currents
- If you remove the tickler the voltage across the potential coil will be cut in half
6
Q
Describe a three phase, four wire, wye connected service
A
- Can provide power for both three phase and single phase
- 7 jaws
- Used in three phase services of 200A or less
7
Q
Describe a three phase, four wire, delta service
A
- Can provide three phase and single phase power
- Contains a high leg (A phase) which must be separated by a barrier
- 7 jaws
- High leg is always on the right side of the meter
8
Q
What are the 2 types of instrument transformers
A
Potential transformers and current transformers
9
Q
Describe a potential transformer
A
- Isolate a voltmeter from the high voltage of the circuit being tested
- They reduce the voltage to the voltmeter
- Standard rated secondary voltage is 120V
10
Q
Describe a current transformer
A
- Reduces the current to a safe and manageable value
- Transfers energy from one circuit to another while maintaining isolation between circuits
- Connected in series with the load
- Standard rating current for revenue metering is 5A
- Acts as a step up transformer
11
Q
What are 3 types of CT’s
A
- Wound-Primary (both the primary and secondary windings wrapped around a common core)
- Bar-type (a single primary conductor permanently passing through a core and a secondary winding wrapped around the same core)
- Toroidal (shaped like a donut)
12
Q
When must CT’s have their secondary windings grounded
A
- When the primaries of the CT are connected to circuits of 300V or greater
- They are mounted on switchboards
13
Q
Is the secondary of an energized CT open or close circuited
A
Close circuited
14
Q
Describe a voltmeter transfer switch
A
- Has eight positions
- Is able to read 3 line and 3 phase voltages of a wye system with a single voltmeter
- It’s a break before make
15
Q
Describe an a meter transfer switch
A
- Is a make before break action to ensure the CT secondary is always close circuited
