Introduction to 3-Phase Meters. Northwest Electric Meter School August 21,2017 Adam Schwab ~ Meter/Relay Tech. Grant County PUD

Transcription

1 Introduction to 3-Phase Meters Northwest Electric Meter School August 21,2017 Adam Schwab ~ Meter/Relay Tech. Grant County PUD 1

2 Meter Pulling device Objectives Provide a brief overview of polyphase meters Provide a basic description of electromechanical meter construction and operation Introduce the meter constant calculation for electromechanical meters Provide a short introduction to the meter form and wiring connections 2

3 Introduction The 3-phase meter functions under the same principles as the single phase meter. A 3-phase meter is basically 3 single phase meters combined in one meter. Can measure kilowatt hour consumption or kilowatt demand or both. Blondel s Theorem In a system of N current carrying conductors, N-1 elements, properly connected, will measure the power used. All voltage coils must have a common tie to the conductor in which there is no current coil. 3

4 Base Design A Base meter All connections to meter are made on the bottom of the base which can t be detached from the meter. Requires no socket or base. S Base meter (Socket) All connections to the meter are made to the meter socket, which enables you to change out the meter without rewiring. K Base meter All connections are made to socket. The meter has bus attached to the back which has to be bolted into the base. Switchboard meter All connections are made to switchboard meter case, meter simply slides out and can be replaced very easily. A -BASE 4

5 A-BASE CONVERSION A Base Meter 5

6 S(Socket) Base meter, socket and test switch K - Base 6

7 Switchboard Meter Measuring Capacity Self Contained Class 100 Class 200 Class 320 Class 480(K-base) Transformer rated (CT Meter) Class 10 Class 20 7

8 Electromechanical Types Hybrid Typically electromechanical meter with an electronic demand register. Solid State / Electronic Prove the meter constant (Kh x Rr x Rs) / 10,000 = Meter Constant Kh = Watthour constant. The number of watthours represented by one revolution of the disk. Rr = Register ratio. The number of revolutions of the gear which meshes with the disk shaft, per complete rotation of the fastest dial pointer. Rs = Shaft gear reduction (first reduction). The number of revolutions of the disk rotor shaft per complete revolution of the gear it engages. 8

9 Get Kh, Rr and Model # Metering Symbols Kh Watthour constant. The number of watthour per disk revolution. Rs Shaft gear reduction (ratio between rotor shaft and first gear ) 9

10 Shaft Reductions Get Rs for the meter Some Common Meter Forms and Possible connections. Meter forms are defined in ANSI standard C

11 Form 9S 4Wire CT Rated Wye Form 9 wiring example 11

12 Form 5S 3 or 4 wire service Wye or Delta CT rated Form 5S wiring example 12

13 Form 6S 4 Wire Wye CT rated Z-coil Form 6S wiring example 13

14 Form 8S 4 Wire Delta CT rated Form 8S wiring example 14

15 Form 12S 3 Wire Wye or Delta Self contained Form 12S wiring example 15

16 Form 15S 4 Wire Delta Self contained Form 15S wiring example 16

17 Form 16S 4 Wire Wye Self contained Form 16S wiring example 17

18 Form 14S 4 Wire Wye Self contained Z-coil Two half turns Electromechanical Basics Voltage is passed through a potential coil. Current is passed through a current coil. Current and voltage fluxes are created and combined to produce torque on the disk and cause rotation. 18

19 Electromechanical Meters An aluminum Laminated disk Rotor Creep holes Worm Gear on shaft. (Single cut or double) Magnetic bearings are on top and bottom, and suspend the disk, minimizing friction. (or jewel bearings) The sectored disk restricts eddy currents induced in the disk from reacting with the flux of other stators. Stators (2, 2.5, 3) A stator is formed by a potential coil and a current coil. Electromechanical Meters cont. Magnetic Shields Placed around the voltage coils prevent leakage flux from reacting with the wrong eddy currents and causing metering errors. Current coil shields Made of plastic To isolate technician from voltage during adjustment. Potential coil lights Indicate that voltage is present Can be incandescent or Led Voltage ranges are often narrow. 19

20 Electromechanical Meters cont. Mechanical register. Many intricate gears Acts like an adding machine and accumulates the revolutions of the disk. Pointer style or cyclometer. Can be calibrated and repaired in the shop or field. There are adjustment screws for Full Load, Light Load and Power Factor. Are sometimes heavy due to amount of metal parts. Light Load Adj. Magnetic shield Power Factor Adj. Full Load Adj. 20

21 Magnetic Bearing Register Potential Coil Sectored Disk Current Coil Retarding Magnet Potential indicating Light 21

22 Demand Motor Demand Register Kilowatt hour Register Electronic Basics Current is passed through a current sensor. (Small CT) Voltage is measured with the equivalent of a digital multimeter. The voltage, current and angle are mathematically computed to find kilowatt hour consumption. The values are then displayed on the LCD screen. Much more information is available. Much more accurate then electromechanical meter at very light loads. (No friction from register or disk) 22

23 Electronic Meters Automatic-wide voltage range LCD display and register Voltage indicators for each phase Current sensors No moving parts to wear out Lightweight and easily handled Electronic Meters cont. Need to be factory calibrated and repaired (some first generation meters had some adjustments) Auto detect wye or delta Multiple form replacement Electronic > Mechanical 45S = 5S 9S = 8S and 9S (6S requires moving C phase potential) 16S = 14S, 15S And 16S 23

24 Electronic Meters cont. Site survey software Per phase values for: Voltage and voltage angle Current and current angle Power factor Total harmonic distortion Much more can be available Diagnostics for many conditions, with user adjustable thresholds. Electronic Meter 24

25 Electronic Meter Brains Current Sensor 25

26 Switchboard Meters Commonly used in substation metering With both current transformers and voltage transformers. Commonly contain a modem for remote interrogation. KYZ outputs for customer or SCADA indication. (Supervisory Control And Data Acquisition) Bidirectional (4 Quadrant) metering 26

27 Switchboard Meter Switchboard Meter Case 27

28 Switchboard Meter 28

29 Can you guess which form #? Lightning arrestors 29

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