Electrical Grid 2: Chapter 2 - Three-Phase Power - Possible Test Questions - WEEK 8 Flashcards
Generating three-phase power is similar to generating:
- single-phase power; the only difference is that instead of one coil of wire, there are three. To better illustrate the principle we will show a different type of magnet.However, the principle remains the same.
Each coil of wire on the generator will produce:
- Its own voltage and current. The voltage and current on each coil will be 120 degrees out of phase with the others. This produces a three-phase sine wave.
Three-phase power results in:
- much smoother and more efficient operation of equipment. Because three-phase power delivered to a load is constant, the three phase load can be much smaller than a single-phase load while providing the same output.
The three coils of a three-phase generator can be connected in:
- either a DELTA configuration or a WYE configuration.
In a WYE system, coil current and phase current remain:
- the same.
In a DELTA system, the system voltage is the same as:
- the coil voltage.
Delta and three-wire Wye systems look:
- the same in the field. Both have three phases and carry no neutral.
The four-wire WYE system is the most:
- widely used system.
In the field, three-wire WYE systems and DELTA systems are:
- identical in appearance.
All of the generators connected to a regional transmission network are all:
- at the same angle of rotation at any given time.
When the phase sequence (shown as ABC in the graphic above) is maintained throughout the system:
- three-phase motors will spin in the same direction as the generator.
If the phase sequence is unchanged:
- rotation will remain unchanged.
If any two phases are reversed:
- rotation will change.
A phasing meter is a high voltage voltmeter used for:
- proving phase sequence. The meter consists of a phasing probe and a meter probe, which attach to hot sticks. An insulated jumper connects the two probes.
Phasing meters are used to ultimately prove that:
- the sequence has not changed.