Single-Phase Meter Components - SaskPower 3 Book 1/8. SINGLE-PHASE ME… · energy meter. This...

March 2, 2005

S T U D E N T M A N U A L

Single-Phase Meter Components

Copyright 2004 by the Training and Development Centre, SaskPower. All Rights Reserved

2 S T U D E N T T R A I N I N G M A N U A L

Prerequisites:

• None

Objectives: From memory, you will be able to explain the parts and function of a single-phase meter.

Rationale: The measurement of a customer’s consumption is calculated by an energy meter. This module will help in the installation, maintenance and troubleshooting of single-phase metering in order to avoid loss of utility revenue.

Learning Objectives

• Explain the requirements to measure electrical energy.• Describe the parts of an energy meter.• Describe the operating principle of an energy meter.• Describe the five types of single-phase meters and their application.• Describe the function of the inherent meter multiplier.

Learning Methods

• Self-learning + On-the-job• Self-learning + On-the-job• Self-learning + On-the-job• Self-learning + On-the-job• Self-learning + On-the-job

EVALUATION METHODS

• Written test• Written test• Written test• Written test• Written test.

S I N G L E - P H A S E M E T E R C O M P O N E N T S 3


STUDENT RESOURCES

• None

Learning Steps

1. Read the Learning Guide.2. Follow the steps outlined in the Learning Guide.3. Clarify any questions or concerns you may have.4. Complete the Practice and Feedback.5. Complete the Evaluation.



Lesson 1: Requirements to Measure Electrical EnergyLearning Objective:Explain the requirements to measure electrical energy.Learning Method:Self-learning + On-the-jobEvaluation Method:Written test

Watt-Hour Meter

Watt-hour meters are used by power companies to determine the amountof energy used by a customer. This is essential since the customer ischarged for the amount of energy used.

A watt-hour meter measures the amount of power consumed

(P = E x I) and multiplies this value by the amount of time it has beenconsumed.

Energy = Power (watts) x Time (hours)

Therefore, a watt-hour meter measures watt/hours or kWh.



Lesson 2: Components of an Energy MeterLearning Objective:Describe the parts of an energy meter.Learning Method:Self-learning + On-the-jobEvaluation Method:Written test

Cover

The cover is made of clear glass or Lexan type plastic and serves threefunctions:

• encloses the meter• seals the meter to prevent moisture from entering the metering

components• prevents tampering

Terminals

Lugs found at the rear of the meter are used to make the connectionsbetween the line and load, as well as the internal parts of the meter.

Frame

The frame is simply used for mounting the different components of themeter securely.

Aluminum Disc

An aluminum disc can be seen through the glass cover of the meter,revolving in a left to right direction. This disc is connected to a registerby means of a gear train and records the number of kilowatt-hoursconsumed over a specific period of time.

---Note---A meter with a cracked or broken cover should be changedimmediately upon discovery and sent in to meter repair fortesting and reparations.



Register

The register records the number of aluminum disc turns. For everyrevolution, the disc represents a definite number of watt-hoursconsumed. The amount of energy (watt-hours) per revolution of the discis called the watt-hour constant and is represented by the symbol kh.This kh factor is established when calibrating the meter and is identifiedon the register of the meter itself.

If a meter had a kh of 4/5, this would indicate 4 watt-hours consumedfor every five revolutions of the disc.

As it is not practical to measure energy in watt-hours due to the averageconsumption of our customers, the meters are engineered to recordconsumption in kilowatt-hours (kWh).

The register consists of dials from which the kWh are read and holds thegears connecting the disc to the dials. Generally, the type of registerused is the clock type.



Lesson 3: Operating Principles of an Energy MeterLearning Objective:Describe the operating principle of an energy meter.Learning Method:Self-learning + On-the-jobEvaluation Method:Written test

Introduction

A watt-hour meter is identical to that of a wattmeter consisting of apotential coil and a current coil. However, in a watt-hour meter, themagnetic fields of the current and potential coils are used to drive asmall electric motor rather than move a pointer across a scale. The rotor



of this miniature motor is the aluminum disc.

---Note---The disc is driven by opposing magnetic fields from the potentialand current windings.



Lesson 4: Types of Single-Phase MetersLearning Objective:Describe the five types of single-phase meters and their

application.Learning Method:Self-learning + On-the-jobEvaluation Method:Written test

Single-Phase 2-Wire Circuit Meter

The single-phase 2-wire circuit meter consists of a single current coiland a single potential coil that uses a single line voltage (usually 120V)to measure the amount of power consumed. Since current and voltageare in phase with each other, there is no need to illustrate the relationshipwith vectors.

As can be seen from the above circuit diagram, the current coil of themeter measures the current flowing through the customer’s load. Thevoltage coil of the meter measures the voltage across the customer’sload.



Example:

Single-Phase 3-Wire Circuit (120/240V) Meter

Single-phase 3-wire circuit meters measure the line to line voltage of

---Note---A red warning label may be on the face of the meter to identifythat the meter is a 120 volt and is to be used only on a 2-wirecircuit.



240 volts using a coil connected line to line. The load current ismeasured using two half coils. Half coils are implemented to gainaccuracy in averaging the current flow on each hot leg.

Example

In this case, the customer’s load would be 2,400W.

Meter Registers

For an unbalanced condition, the customer load is connected across 120volts (phase-to-neutral). The meter is still connected across 240 volts;however, the load passes through only one of the meter’s half coils.

Example:

Customer:

Meter:



Types of Meters

There are various types of meters used to measure consumer usage.Two common meters used in conjunction with instrument transformersare the instrument rated meter and the network meter.

Instrument Rated Meter

The instrument rated meter is used for 120V circuits with loads of50kVA or greater. The current coils of the meter are replaced with acurrent transformer, also containing half-coils which deliver a measuredportion of load current to the meter at the 5 amp level. These currenttransformers are sized in ratios such as 200:5 and 400:5 (400 amps ofline current to 5 amps of maximum measured current in the meter).Because of the ratio effect, a multiplier external to the meter is requiredto calculate the actual amount of power consumed. Instrument ratedmeters can be identified by a yellow box with a black X in it.

Network

The network meter is a specialty meter used where 120/240V single-phase service is not available, but 120/208V single-phase is availableand acceptable to the customer. This meter is distinguished by a fifthjaw or terminal lug located on the left-hand side of the meter facing thefront. It is between the top and bottom terminals and runs horizontallyinstead of the traditional vertical terminal.

CAUTION

Do not use this meter on 120/240V services due topotential metering inaccuracies.



Lesson 5: Inherent Meter MultipliersLearning Objective:Describe the function of the inherent meter multiplier.Learning Method:Self-learning + On-the-jobEvaluation Method:Written test.

Introduction

A four dial kWh meter will read up to 9,999 kWh and will start over atzero once it has cycled.

Meters are read once every month or every three months. If such a meterwere connected to a load where consumption was more than 10,000kilowatt-hours, meter readers would be left confused, to say the least.

To avoid this problem, an inherent or built-in multiplier is used to slowdown the dial movement on the meter. This is possible by way of a gear,mounted between the disc and the register.

For example, if an inherent meter multiplier is ten, the meter wouldrecord only one kilowatt-hour for every ten kilowatt-hours consumed.

For all meters where an inherent multiplier is used, the multiplier ismarked on the face of the meter or, quite often, on the glass meter cover.

In order to obtain the correct number of kilowatt-hours used in a periodof time, multiply the dial readings by the meter multiplier.

For example, a meter has an inherent multiplier of 10:

Present reading: 8810

Previous reading: 8767

Consumption = 43 x 10 (inherent meter multiplier)

Consumption = 430 kilowatt-hours

---Note---A meter with five dials can also be used to accomplish the samething as a meter with an inherent multiplier of x10.



Summary

To summarize this module, you have learned:

• The requirements to measure electrical energy.• The parts of an energy meter.• The operating principle of an energy meter.• The five types of single-phase meters and their application.• The function of the inherent meter multiplier.

Practice Feedback

Review the lesson, ask any questions and complete the self test.

Evaluation

When you are ready, complete the final test. You are expected toachieve 100%.



Review Questions

1. The requirements needed to measure electrical energy are:

(a) Resistance and power.

(b) Power and time.

(c) Amperage and voltmeters.

(d) Time and resistance.

T / F 2. A wattmeter consists of a current coil connected in series with the circuit, and a potential coil connected in parallel across the circuit.

3. A wattmeter reads:

(a) Apparent power.

(b) Reactive power.

(c) True power.

(d) None of these

T / F 4. Electrical energy is the product of the rate measured in Vars multiplied by the current measured in amps.

5. The meter used by power companies to calculate the amount of energy used by a customer is:

(a) A voltmeter.

(b) A watt-hour meter.

(c) A wattmeter.

(d) An ammeter.

6. The power factor of a circuit is 95% and the apparent power is 560kVA. The true power of the circuit is:

(a) TP = 532kW.

(b) TP = 532kVA.

(c) TP = 560kW.

(d) TP = 577kW.

T / F 7. The amount of energy (watt-hours) per disc revolutions is called the watt-hour constant and is represented by the symbol kh.



T / F 8. The magnetic field of the current and potential coils are used to drive a small electric motor in a watt-hour meter.

T / F 9. The aluminum disc and potential coils are used to drive a small electric motor in a watt-hour meter.

10. A 120/208V single-phase service is metered using a:

(a) Network meter.

(b) Instrument rated meter.

(c) A-base meter.

(d) All of these

11. A 120V single-phase service with 110A of current is metered using a:

(a) Network.

(b) 2-wire single-phase meter.

(c) 3-wire single phase meter.

(d) Instrument rated meter.

12. A 100 amp residential 120/240V service is metered using a:

(a) 2-wire single-phase meter.

(b) Instrument rated meter.

(c) 3-wire single-phase meter.

(d) All of these

13. A 60kVA single-phase 120V service is metered using a:

(a) 2-wire single phase meter.

(b) A base meter.

(c) An instrument rated meter.

(d) None of these

T / F 14. An inherent meter multiplier is used to slow down the dial movement on the meter.



15. A meter with an inherent meter multiplier of 5 has a present reading of 0015, the previous months reading was 9938. How many kilowatt-hours has this service used?

(a) 77kWh

(b) 385kWh

(c) 9923kWh

(d) 7700kWh



Review Question Solutions

1. Power and time.

2. T

3. True power.

4. F

5. A watt-hour meter.

6. TP = 532kW.

7. T

8. T

9. F

10. Network meter.

11. 2-wire single-phase meter.

12. 3-wire single-phase meter.

13. An instrument rated meter.

14. T

15. 385kWh

Single-Phase Meter Components - SaskPower 3 Book 1/8. SINGLE-PHASE ME… · energy meter. This...

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