Services. Three Phase Service

Transcription

1 Services Primary Service vs Secondary Service Overhead vs Underground Common Service Types Three Phase Wye Closed Open Delta Corner Grounded Center Tapped Open Single Phase Three Phase Service Wye Delta Corner Grounded Center Tapped Open 1

2 Wye Service Customers needing three phase for some equipment and also having large amounts of single phase load Many small commercial & industrial buildings 208/120 Wye phase 120 single phase 480/277 Wye 480 three phase 277 single phase 3 Phase Wye System 3 wires connect all at a common point which is grounded. End points become the connection points for the 3 phases. Y system wye 2 separate voltages Phase to Phase Phase to Ground 2

3 208/120 Wye Smaller customers requiring mostly single phase and some 3 phase. 480 volt services are more economical for larger motor loads. 480/277 Wye Voltages 480 volts phase to phase 277 volts phase to ground Requires step down transformer to produce 120 volts for receptacles 277 volt lighting fixtures are available 3

4 3 Phase Delta Systems Generally built to areas with mostly 3 phase load and not much single phase load. (oil pumping, irrigation, etc.) Advantages: Expense of one less wire to build and maintain. Disadvantage: Unbalanced voltages from amounts of single phase load. Phases connected end to end Each phase relies on the sharing of one wire as a supply and return path for the others. Voltage the same between any 2 wires Popular for ungrounded systems Center-Tapped Delta Customers with mostly three phase equipment and very little single phase equipment. Manufacturing & processing facilities 240/120 CT Delta Smaller 3 Phase Services with mostly 3 phase load. 240 three phase C 120 single phase 480/240 CT Delta Larger 3 Phase Services with mostly 3 phase load. 480 three phase 240 single phase High or Wild Leg A G B Neutral Wire 4

5 Corner Grounded Delta 240 or 480 volts. Usually only for 3 Phase Motor/Pumping Load. A Oil Pumps Irrigation Pumps Municipal Water G C B Open Delta Uses only 2 transformers Often from a V- Phase Distribution Line. Wye with 2 Phases and a Neutral. Less Expensive Light 3 Phase A C N a b c n Open Wye Primary to Open Delta Secondary Open Wye (V Phase) Primary H1 H2 H1 H2 X1 X3 X1 X3 X2 X2 3 Phase 4 Wire Open Delta Secondary: 120/240, 240/480, etc for lights and power 5

6 Single Phase Service 120/240 volt service. Neutral attached to center bushing in transformer. 120 volts Hot to Neutral 240 volts Hot to Hot Single Phase from 3 Phase Systems Individual single phase loads can be connected and balanced to resemble a 3 phase load. Voltages will be different in Wye & Delta systems If not balanced, voltage unbalances will result. 6

7 Secondary System Transformer Service Drop Meter Loop Meter Ground Rod Main Breaker Box Circuits Service Drop Overhead: Service Drop Underground: Service Lateral Three Phase: 3 or 4 wires Single Phase: 2 or 3 wires Triplex Quadraplex 7

8 Meter Loop A Meter Loop is comprised of: Weatherhead Service Mast/Riser Meter Base/Can Meter The Cash Register Owned by Utility Installed in customer s equipment. 8

9 Main Disconnect Today, electrical codes require some type of disconnect device (switch) to shut off all the circuits supplied by the disconnect. Usually a Main Breaker in the breaker box. Older or larger facilities may have Main Disconnects rather than main breakers. Ground Wire/Rod Most electrical systems in North America are grounded for safety and lightning protection. Their is generally a ground wire/rod at the: Service transformers. Meter Base Breaker Box Formal Names: Grounding System Conductor (wire) Grounding System Electrode (rod) 9

10 Breaker/Fuse Box Formally called the Service Entrance Panel Provides a location for breakers or fuses to protect the individual circuits in the facility. Some larger customers have Sub-panels which contain breakers and fuses. Feeders circuits supplying services or sub-panels. the service drop is a feeder. Branch Circuits Individual Branch Circuit Circuit to one piece of equipment Appliance Branch Circuit. Circuit to several fixed appliances Lighting Branch Circuit Circuit supplying only lighting fixtures. General Purpose Branch Circuit Circuit to receptacles and lights. Circuits 10