Topic 8 energy and power requirements of AC systems topic b8

Bài giảng ngành Điện: Giải các bài toán trong mạch điện điện thế thấp một pha và ba pha (Phần B) gồm các chủ đề sau Solve problems in single and threephase low voltage circuits Part B Content Topic 1: AC power and power factor Topic 23: Multiphase systems Topic 4: Threephase STAR connection Topic 5: Threephase, Fourwire systems Topic 6: Threephase DELTA connection Topic 7 Interconnected Star and Delta Devices Topic 8 Energy and Power Requirements of AC Systems Topic 9: Harmonics

Solve Problems in Single and Three Phase Low Voltage

Circuits

Topic 8: Energy and Power Requirements of AC Systems

Three-Phase TRUE Power

P3Ø = 3x VPIPCos Ø P

Total True Power in 3Ø

Circuit

P 3Ø = √3 V L I L Cos Ø

Three-Phase Power Triangle

(Ø)

Phase Angle

Three-Phase Power Triangle

Three-Phase Power

 Exercises

1. A 3Ø, 415V motor with an impedance per phase of 15Ω at a pf

of 0.6 lag will consume how much true power when…

 Connected in STAR configuration

 Reconnected in DELTA configuration

2. A 3Ø, 400V motor rated at 12.5kW with a pf of 0.8 lag If the

motor is delta-connected, determine:

 Impedance per phase

 True power if reconnected in STAR

Three-Phase Power

Exercise 3

A balanced 3-phase load has the measurements recorded as per the diagram Determine the following:

1) P consumed by load2) Pf of the load

3) Q of the load4) Would a 10kVA alternator be suitable to supply this load?

ZA ZB ZC

L1 L2 L3 N

W AV

2464W 16A220V

Methods of Correcting Power

Factor:

Three Phase Installations

 Ensuring that all motors and transformers are correctly loaded

 Adding capacitance to an installation (that is inductive)

Energy and Power

Requirements of AC Systems

Power Measurement

Three-P 3Ø = P A + P B + P C Unbalanced Load

Three-P 3Ø = W 1 + W 2 Balanced Load Only

W2

Three-Phase Power

Measurement

 TWO-Wattmeter Method (cont)

 Power Factor Calculation

 Step 1: Use Two-Wattmeter method

 Tan Ø = √3 (W2 – W1)

 Step 2: Use Transposition to Find Ø

 Ø = Tan-1(above number)

 Step 3: Find Power factor

 Pf = Cos Ø

2 Pf of load

3 Apparent power flowing from supply

4 Reactive power oscillating in load

Three-P 3Ø = W 1 + W 2 + W 3 Balanced OR Unbalanced Load

Artificial Star-point

Energy and Power

Requirements of AC Systems

Purpose for Energy Measurement

Three-Phase Energy and Power Measurement

 Purpose for Energy Measurement

 Revenue Raising

 Monitoring and billing for the energy usage of the

customer

 Planning and design requirements

 Monitoring the total load required for a given area to

ensure sufficient supply is available

 Power factor specifications

 Ensuring the existing infrastructure is utilized to its

highest capacity

Three-Phase Energy and Power Measurement

 Induction-disc type or

Electronic

Three-Phase Energy and Power Measurement

 Types of Measurement

Instruments

 Maximum Demand Indicator

 Measures the highest

apparent power occurring within a set time frame – for the purpose of determining tariff level

 Power Factor Meter

 Measures phase

relationship between supply voltage and current – for the purpose of determine tariff level

Three-Phase Energy and Power Measurement

Three-Phase Energy and Power Measurement