BEE2133 Electrical Machine

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BEE2133 Electrical Machine Power
SystemChapter 6 Cost of Electricity
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CHAPTER GUIDELINE

• Introduction
• Electricity Tariff
• - energy tariff
• - demand tariff
• - comparison of Malaysia Tariff with other
  countries
• ? power factor tariff
• Energy efficiency

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INTRODUCTION

• The production, transmission and distribution of
  energy involves important costs-
• fixed costs
• operating costs

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INTRODUCTION

• Based on the two types of cost, utility companies
  have established rate structures that attempt to
  be as equitable as possible for their customers.
• The rates are based upon the following
  guidelines-
• The amount of energy consumed (kWh)
• The demand, or rate which energy is consumed (kW)
• The power factor of the load

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INTRODUCTION

• Fixed costs - depreciation charges against
  buildings, dams, turbines, generators, circuit
  breakers, transformers, transmission lines and
  other equipments used in the production,
  transmission and distribution of electrical
  energy.
• Operating costs salaries, fuel costs,
  administration and any other daily or weekly
  expense.

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Tariff based upon energy and demand
ELECTRICITY TARIFF

• Malaysia and US uses both energy and demand
  tariff.
• Energy Tariff-
• Depends on-
• Amount of energy used
• Service charge
• Applies to all sectors (i.e. low, medium and high
  power users)

• Cost per kW-
• USA decreases when used more
• Malaysia increases when used more!!!

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TARIFF BASED UPON ENERGY AND DEMAND
ELECTRICITY TARIFF

• Demand Tariff
• Tariff for large consumers (i.e. factories)
• Includes-
• Energy consumed (kWh)
• The rate at which it is used (kW)
• Maximum active power / maximum demand

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TARIFF BASED UPON ENERGY AND DEMAND
ELECTRICITY TARIFF

• Why demand tariff? (Example)
• Two factories (A and B) connected to transformer
  A (TA) and transformer B (TB) respectively.
• Factory A operates night and day constantly
  drawing 1000kW of active power.

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TARIFF BASED UPON ENERGY AND DEMAND
ELECTRICITY TARIFF

• Why demand tariff? (Example)
• Factory B consumes the same amount but its load
  is changing between 50kW and 3000kW.
• Capacity of transformer and the transmission line
  supplying factory B must be greater than factory
  A.
• Thus utility company must invest more to service
  factory B. Thus factory B must pay more.

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DEMAND METER
ELECTRICITY TARIFF

• Why factory A does not liable to be paid for high
  maximum demand although the maximum demand while
  motor starts-up is high?
• Why factory B liable to be paid for high maximum
  demand and not A?

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DEMAND METER
ELECTRICITY TARIFF

• For demand tariff to be used, several factors
  should be considered.
• Main consideration demand interval. Only if the
  maximum demand has a demand interval which is
  determined by the utility. Usually the period is
  10, 15 or 30 minutes.

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DEMAND METER
ELECTRICITY TARIFF

• The demand meter is used to monitor the power
  drawn by the plant.
• It automatically measures the average power
  during successive demand interval (i.e.15
  minutes).
• The average power recorded during the interval is
  called the demand.
• The meter will record the highest demand during
  each month.
• This demand is used for both diagnostic and
  billing purposes.

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EXAMPLE 1

• The graph represents the active power drawn by a
  large factory between 700 and 900 in the
  morning. The demand meter has a 30 min demand
  interval. Let us assume that at 700 the first
  pointer (the current demand counter) reads 2MW
  while the second (the maximum demand counter)
  pointer indicates 3MW. What are the meter
  readings at the following times?
• 730
• 800
• 830
• 900

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EXAMPLE 1
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EXAMPLE 1 (solution)

• At 730-
• Average power 2MW
• Pointer 1 still indicate 2MW
• Pointer 2 still indicate 3MW
• At 800-
• Average power (7MW x 5 min 2MW x 5 min 4MW x
  20 min) / 30 min 4.17MW
• Pointer 1 moves to 4.17MW
• Pointer 2 is pushed by pointer 1 to 4.17MW

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EXAMPLE 1 (solution)

• At 830-
• Average power (7 x 5 8 x 5 4 x 5 3 x 5
  5 x 5 1 x 5) / 30 4.67MW
• Pointer 1 moves to 4.67MW
• Pointer 2 is pushed by pointer 1 to 4.67MW
• At 900-
• Average power (1 x 5 12 x 5 1 x 20) / 30
  min 2.83MW
• Pointer 1 moves to 2.83MW
• Pointer 2 still indicate 4.67MW

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TARIFF BASED UPON POWER FACTOR
ELECTRICITY TARIFF

• Industries which uses many ac machines absorbs
  reactive power to produce their magnetic fields.
• Thus, the power factor is not unity.
• A low power factor increases the cost of
  electrical energy.
• Malaysia does not have tariff based upon power
  factor.
• Industries in Malaysia must maintain a near unity
  power factor or pay the fines.
• USA has tariff based upon power factor.
• In US, if 90 of the highest average kVA measured
  during any 30-minutes period is higher than the
  maximum demand, the amount will be used as
  billing demand (replaced maximum demand)

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TYPICAL RATE STRUCTURES (TARIFF)
ELECTRICITY TARIFF

• Malaysias tariff categories-
• Domestic Tariff - applies to consumers occupying
  private dwellings, which are not used to carry
  out any business.
• Commercial Tariff - applies to consumers
  occupying or operating premises for commercial
  purposes.
• Industrial Tariff - applies to consumers engaging
  in manufacturing, quarrying and pumping for water
  treatment plant.

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TYPICAL RATE STRUCTURES (TARIFF)
ELECTRICITY TARIFF

• Malaysias tariff categories (cont.)-
• Mining Tariff - applies to consumers utilizing
  most part of electricity consumed for extracting
  minerals.
• Street Lighting Tariff - applies to consumers
  utilizing electricity for public lighting, neon
  and floodlighting.
• Top-up and Standby Services - applies to
  Co-generators utilizing a single primary energy
  source to generate sequentially two different
  forms of useful energy.

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TYPICAL RATE STRUCTURES (TARIFF)
ELECTRICITY TARIFF

• Malaysias tariff categories (cont)-
• Special Agricultural Tariff - applies to
  consumers conducting specific agricultural
  activities strictly related to agriculture
  cultivation and breeding. The activities are
  confined to agriculture livestock (poultry and/or
  hatching, cattle and/or dairy, rearing of other
  animals), aquaculture (the breeding and
  cultivation of water plants and animals),
  horticulture (growing of fruits, vegetables and
  flowers) and pumping for irrigation/drainage of
  land for controlling water gates for the
  production of grains such as padi.

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TYPICAL RATE STRUCTURES (TARIFF)
ELECTRICITY TARIFF

• Malaysian Domestic Tariff-
• - applies to consumers occupying private
  dwellings, which are not used to carry out any
  business.

Source http//www.tnb.com.my/tariff. Accessed on
30 March 2009
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ELECTRICITY TARIFF

• Malaysian Commercial Tariff-
• - applies to consumers occupying or operating
  premises for commercial purposes

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TYPICAL RATE STRUCTURES (TARIFF)
ELECTRICITY TARIFF

• Malaysian Industrial Tariff-
• - applies to consumers engaging in
  manufacturing, quarrying and pumping for water
  treatment plant.

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TYPICAL RATE STRUCTURES (TARIFF)
ELECTRICITY TARIFF

• Malaysian Industrial Tariff (cont.)-

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TYPICAL RATE STRUCTURES (TARIFF)
ELECTRICITY TARIFF

• Malaysian Industrial Tariff (cont.)-

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COMPARISON BETWEEN MALAYSIA TARIFF US TARIFF
ELECTRICITY TARIFF

• US tariff categories defers from each of its
  utility companies.
• Typical USs tariff categories-
• Domestic Power power corresponding to the needs
  of houses and rented apartments.
• Small Power power less than 100kW.
• Medium Power - power between 100kW to 5MW.
• Large Power power exceeds 5MW

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COMPARISON BETWEEN MALAYSIA TARIFF US TARIFF
ELECTRICITY TARIFF

• Example of US Domestic/Residential Tariff-

Source Wildi , Theodore, Electrical Machines ,
Drives ,and Power System, 5th Edition,
Prentice-Hall, 2002
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COMPARISON BETWEEN MALAYSIA TARIFF US TARIFF
ELECTRICITY TARIFF

• Example of US General Power (Medium Power)
  Tariff-

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COMPARISON BETWEEN MALAYSIA TARIFF US TARIFF
ELECTRICITY TARIFF

• Example of US General Power (large power) Tariff-

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EXAMPLE 2

• A homeowner consumes 900kWh during the month of
  August.
• Calculate the electricity bill using Malaysias
  Domestic tariff.
• Calculate the electricity bill using the US
  residential rate schedule.

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EXAMPLE 2 (solution)

• Malaysias Domestic tariff.
• First 200kWh _at_ 21.8sen/kWh RM 43.60
• 700kWh _at_ 28.90sen/kWh RM202.30
• TOTAL
  RM245.90

• US residential rate schedule.
• Minimum monthly charge 5.00
• First 100kWh _at_ 5sen/kWh 5.00
• Next 200kWh _at_ 3sen/kWh 6.00
• Next 600kWh _at_ 2sen/kWh 12.00
• TOTAL
  28.00

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EXERCISE 1

• A medium voltage industry operating night and
  day, 7 days a week, consumes 260,000kWh per
  month. The maximum demand is 1200kW.Calculate the
  electricity bill using Malaysias Medium Voltage
  General Commercial tariff.

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EXERCISE 2

• A small industry operating night and day, 7 days
  a week, consumes 260,000kWh per month. The
  maximum demand is 1200kW and the maximum kVA
  demand is 1700kVA. Calculate the electricity bill
  using US medium power rate schedule.

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• THANK YOU
• FOR YOUR ATTENTION!