Calculate Transformer Losses (As per Test Results)


111

  • Calculate Form Factor at Full Load & Actual Load.
  • Calculate Core Losses at Full Load & Actual Load.
  • Calculate Copper Losses at Full Load & Actual Load.
  • Calculate Stray  Losses at Full Load & Actual Load.
  • Calculate Total Losses at Full Load & Actual Load.
  • Calculate Transformer Efficiency  at Full Load & Actual Load.

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Indian Electricity Rules-Abstract


Abstract of Indian Electricity Rules:

1)    Cut-out on consumer’s premises:

  • The supplier shall provide a suitable cut-out in each conductor of every service-line other than an earthed or earthed neutral conductor or the earthed external conductor of a concentric cable within a consumer’s premises, in an accessible position. Such cut-out shall be contained within an adequately enclosed fireproof receptacle.
  • Where more than one consumer is supplied through a common service-line, each such consumer shall be provided with an independent cut-out at the point of junction to the common service
  • Every electric supply line other than the earth or earthed neutral conductor of any system or the earthed external conductor of a concentric cable shall be protected by a suitable cut-out by its owner
  • No cut-out, link or switch other than a linked switch arranged to operate simultaneously on the earthed or earthed neutral conductor and live conductors shall be inserted or remain inserted in any earthed or earthed neutral conductor of a two wire-system or in any earthed or earthed neutral conductor of a multi-wire system or in any conductor connected thereto with the following exceptions:(a) A link for testing purposes, or (b) A switch for use in controlling a generator or transformer.

2)    Danger Notices:

  • The owner of every medium, high and extra-high voltage installation shall affix permanently in a conspicuous position a danger notice in Hindi or English and the local language of the district, with a sign of skull and Bones on
  • (a) Every motor, generator, transformer and other electrical plant and equipment together with apparatus used for controlling or regulating the same;
  • (b) All supports of high and extra-high voltage overhead lines which can be easily climb-upon without the aid of ladder or special appliances.

3)    Cables :

  • Flexible cables shall not be used for portable or transportable motors, generators, transformer rectifiers, electric drills, electric sprayers, welding sets or any other portable or transportable apparatus unless they are heavily insulated and adequately protected from mechanical injury.
  • Where the protection is by means of metallic covering, the covering shall be in metallic connection with the frame of any such apparatus and earth.
  • The cables shall be three core type and four-core type for portable and transportable apparatus working on single phase and three phases supply respectively and the wire meant to be used for ground connection shall be easily Identifiable
  • Where A.C. and D.C. circuits are installed on the same support they shall be so arranged and protected that they shall not come into contact with each other when live.

4)    Safety:

  • Two or more gas masks shall be provided conspicuously and installed and maintained at accessible places in every generating station with capacity of 5 MW and above and enclosed sub-station with transformation capacity of 5 MVA and above for use in the event of fire or smoke.
  • Provide that where more than one generator with capacity of 5 MW and above is installed in a power station, each generator would be provided with at least two separate gas masks in accessible and conspicuous position.

5)    High Voltage Equipment installations

  •  High Voltage equipment shall have the IR value as stipulated in the relevant Indian Standard.
  • At a pressure of 1000 V applied between each live conductor and earth for a period of one minute the insulation resistance of HV installations shall be at least 1 Mega ohm Medium and Low Voltage Installations- At a pressure of 500 V applied between each live conductor and earth for a period of one minute, the insulation resistance of medium and low voltage installations shall be at least 1 Mega ohm

6)    Switchboard shall comply with the following provisions :

  • A clear space of not less than 1 meter in width shall be provided in front of the switchboard;
  • If there are any attachments or bare connections at the back of the switchboard, the space (if any) behind the switchboard shall be either less than 20 centimeters or more than 75 centimeters in width, measured from the farthest outstanding part of any attachment or conductor;
  • If the space behind the switchboard exceeds 75 centimeters in width, there shall be a passage-way from either end of the switchboard clear to a height of 1.8 meters.

7)    Declared voltage of supply to consumer:

  • In the case of low or medium voltage, by more than 6 per cent, or;
  • In the case of high voltage, by more than 6 per cent on the higher side or by more than 9 per cent on the lower side, or;
  • In the case of extra-high voltage, by more than 10 per cent on the higher side or by more than 12.5 per cent on the lower side.

8)    Declared frequency of supply to consumer

  • Except with the written consent of the consumer or with the previous sanction of the State Government a supplier shall not permit the frequency of an alternating current supply to vary from the declared frequency by more than 3 per cent.

9)    Meters and other apparatus on consumer’s premises

  • Any meter or maximum demand indicator or other apparatus placed upon a consumer’s premises in accordance with section 26 shall be of appropriate capacity and shall be deemed to be correct if its limits of error are within the limits specified in the relevant Indian Standard Specification and where no such specification exists, the limits of error do not exceed 3 per cent above or below absolute accuracy at all loads in excess of one tenth of full load and up to full load Connection with earth Neutral conductor of a phase, 4 wire system and the middle conductor of a   2 phase, 3-wire system shall be earthed by not less than two separate and distinct connections with a minimum of    two different earth electrodes of such large number as may be necessary to bring the earth resistance to a               satisfactory value both at the generating station and at the sub-station. The earth electrodes so provided, may be interconnected to reduce earth resistance. It may also be earthed at one or more points along the   distribution system or service line in addition to any connection with earth which may be at the consumer’s  premises
  • In the case of a system comprising electric supply lines having concentric cables, the external conductor of such cables shall be earthed by two separate and distinct connections with earth.
  • The connection with earth may include a link by means of which the connection may be temporarily interrupted for the purpose of testing or for locating a fault.
  • All metal castings or metallic coverings containing or protecting any electric supply-line or apparatus shall be connected with earth and shall be so joined and connected across all junction boxes and other openings as to make good mechanical and electrical connection throughout their whole length.

10) Use of energy at high and extra-high voltage

Voltage Ground clearance                     Sectional clearance
11KV    2.75 Meter 2.6 Meter
33KV 3.7 Meter 2.8 Meter
66KV 4.0 Meter 3.0 Meter
132KV 4.6 Meter 3.5 Meter
220KV 5.5 Meter 4.3 Meter
400KV 8.0 Meter 6.5 Meter

11) Transformer:

  • Where transformer or transformers are used, suitable provision shall be made, either by connecting with earth a point of the circuit at the lower voltage or otherwise, to guard against danger by reason of the said circuit becoming  Accidentally charged above its normal voltage by leakage from or contact with the circuit at the higher voltage
  • A sub-station or a switch station with apparatus having more than 2000 litres of oil shall not  be located in the basement where proper oil draining arrangement cannot be provided.
  • Where a sub-station or a switch station with apparatus having more than 2000 litres of oil is installed, whether indoor or out-doors, the following measures shall be taken, namely: –
  • The baffle walls 4[of 4 hour fire rating] shall be provided between the apparatus in the following cases: –
  • (1) Single phase banks in the switch-yards of generating stations and substations;
  • (2) On the consumer premises;
  • (3) Where adequate clearance between the units is not available.
  • Provisions shall be made for suitable oil soakpit and where use of more than 9000 litres of oil in any one oil tank, receptacle or chamber is involved, provision shall be made for the draining away or removal of any oil which may leak or escape from the tanks receptacles or chambers containing the same.
  • The transformer shall be protected by an automatic high velocity water spray system or by carbon dioxide or BCF (Bromo chlorodi feuromethane) or BTM (Bromo tri fluromethane) fixed installation system; and
  • Oil filled transformers installed indoors shall not be on any floor above the ground or below the first basement.
  • Isolators and the corresponding earthing switches shall be interlocked so that no earthing switch can be closed unless and until the corresponding isolator is in open position.
  • When two or more transformers are operated in parallel, the system shall be so arranged as to trip the secondary breaker of a transformer in case the primary breaker of that transformer trips.
  • Where two or more generators operate in parallel and neutral switching is adopted, inter-lock shall be provided to ensure that generator breaker cannot be  closed unless one of the neutrals is connected to the earthing system.
  • Gas pressure type protection to given alarm and tripping shall be provided on all transformers of ratings 1000 KVA and above.
  • Transformers of capacity 10 MVA and above shall be protected against incipient faults by differential protection; and  All generators with rating of 100 KVA and above shall be protected against earth fault/leakage. All generators of rating 1000KVA and above shall be protected against faults within the generator winding using restricted earth fault protection or differential protection or by both.

11)    Connection with earth:

  •  In case of the delta connected system the neutral point shall be obtained by the insertion of a grounding transformer and current limiting resistance or impedance wherever considered necessary at the commencement of such a system.
  • Where the earthing lead and earth connection are used only in connection with earthing guards erected under high or extra-high voltage overhead lines where they cross a telecommunication line or a railway line, and where such lines are equipped with earth leakage relays of a type and setting approved by the Inspector, the resistance shall    not exceed 25 ohms.

12)    Clearance above ground of the lowest conductor

  • No conductor of an overhead line, including service lines, erected across a street shall at any part thereof be at a height of less than:
  • For low and medium voltage lines 5.8 meters
  • For high voltage lines 6.1 metres
  • No conductor of an overhead line, including service lines, erected along any street shall at any part thereof be at a height less than:
  • For low and medium voltage lines 5.5 metres
  • For high voltage lines 5.8 metres
  • No conductor of in overhead line including service lines, erected elsewhere than along or across any street shall be at a height less than:
  • For low, medium and high voltages lines=4.6 meters.
  • For low, medium and high voltage=4.0 meters.
  • For high voltage lines above 11,000 volts=5.2 meters.
  •  For extra-high voltage lines the clearance above ground shall not be less than 5.2 metres plus 0.3 meter for every 33,000 volts or part thereof by which the voltage of the line exceeds 33,000 volts.

Calculate Cable Size and Voltage Drop


Calculate Cable Size and Voltage Drop:

Calculate Voltage Drop and Size of Electrical cable for following data.

  •  Electrical Details: Electrical Load of 80KW, Distance between Source and Load is 200 Meter, System Voltage 415V Three Phase, Power Factor is 0.8,Permissible Voltage drop is  5%, Demand Factor is 1,
  • Cable Laying Detail: Cable is directed buried in Ground in trench at the depth of 1 meter. Ground Temperature is approximate 35 Deg. No of Cable per Trench is 1. No of Run of Cable is 1 Run.
  • Soil Details: Thermal Resistivity of Soil is not known. Nature of Soil is Damp Soil.

Calculation:

  • Consumed Load= Total Load x Demand Factor
  • Consumed Load in KW= 80 x 1 =80KW
  • Consumed Load in KVA= KW/P.F
  • Consumed Load in KVA =80/0.8=100KVA
  • Full Load Current= (KVAx1000) / (1.732xVoltage)
  • Full Load Current= (100×1000) / (1.732×415) = 139Amp.
  • Calculating Correction Factor of Cable from following data :
  • Temperature Correction Factor (K1) When Cable is in Air  is

Temperature Correction Factor in Air :K1

Ambient Temp©

Insulation

PVC

XLPE/EPR

10

1.22

1.15

15

1.17

1.12

20

1.12

1.08

25

1.06

1.04

35

0.94

0.96

40

0.87

0.91

45

0.79

0.87

50

0.71

0.82

55

0.61

0.76

60

0.5

0.71

65

0

0.65

70

0

0.58

75

0

0.5

80

0

0.41

  • Ground Temperature Correction Factor (K2):

Ground Temperature Correction Factor:K2

Ground Temp©

Insulation

PVC

XLPE/EPR

10

1.1

1.07

15

1.05

1.04

20

0.95

0.96

25

0.89

0.93

35

0.77

0.89

40

0.71

0.85

45

0.63

0.8

50

0.55

0.76

55

0.45

0.71

60

0

0.65

65

0

0.6

70

0

0.53

75

0

0.46

80

0

0.38

  • Thermal Resistance Correction Factor (K4) for Soil (When Thermal Resistance of Soil is known):

Ther.Resi Correction Factor: K4

Soil Thermal Resistivity: 2.5 KM/W

Resistivity

K3

1

1.18

1.5

1.1

2

1.05

2.5

1

3

0.96

  • Soil Correction Factor(K4) of Soil (When Thermal Resistance of Soil is not known):

Soil Correction Factor:K4

Nature of Soil

K3

Very Wet Soil

1.21

Wet Soil

1.13

Damp Soil

1.05

Dry Soil

1

Very Dry Soil

0.86

  • Cable Depth Correction Factor (K5):

Cable Depth Factor (K5)

Laying Depth(Meter)

Rating Factor

0.5

1.1

0.7

1.05

0.9

1.01

1

1

1.2

0.98

1.5

0.96

  • Cable Distance correction Factor (K6):

Cable Distance  Correction Factor(K6)

No of Circuit

Nil

cable Diameter

0.125m

0.25m

0.5m

1

1

1

1

1

1

2

0.75

0.8

0.85

0.9

0.9

3

0.65

0.7

0.75

0.8

0.85

4

0.6

0.6

0.7

0.75

0.8

5

0.55

0.55

0.65

0.7

0.8

6

0.5

0.55

0.6

0.7

0.8

  • Cable Grouping Factor ( No of Tray Factor) (K7):

No of Cable/Tray

(Cable Grouping factor K7 )==No of Tray

1

2

3

4

6

8

1

1

1

1

1

1

1

2

0.84

0.8

0.78

0.77

0.76

0.75

3

0.8

0.76

0.74

0.73

0.72

0.71

4

0.78

0.74

0.72

0.71

0.7

0.69

5

0.77

0.73

0.7

0.69

0.68

0.67

6

0.75

0.71

0.7

0.68

0.68

0.66

7

0.74

0.69

0.675

0.66

0.66

0.64

8

0.73

0.69

0.68

0.67

0.66

0.64

  • According to above Detail correction Factors are
  • Ground Temperature Correction Factor (K2) =0.89
  • Soil Correction Factor (K4)=1.05
  • Cable Depth Correction Factor (K5)=1.0
  • Cable Distance correction Factor (K6)=1.0
  • Total De rating Factor= k1x k2 x k3 x K4 x K5 x K6 x K7
  • Total De rating Factor= 0.93

Selection of Cable:

  • For selection of Proper Cable following Conditions should be satisfied
  • (1) Cable De rating Amp should be higher than Full Load Current of Load.
  • (2) Cable Voltage Drop should be less than Defined Voltage drop.
  • (3) No of Run of Cable >= (Full Load current / Cable De rating Current).
  • (4) Cable Short Circuit Capacity should be higher than System S.C Capacity at that Point.

Selection of Cable Case (1):

  • Let’s Select 3.5Core 70 Sq.mm cable for Single run.
  • Current Capacity of 70 Sq.mm cable is 170Amp,Resistance=0.57Ω/Km and Reactance=0.077 mho/Km
  • Total De rating Current of 70 Sq.mm Cable= 170×0.93 =159 Amp.
  • Voltage Drop of Cable= (1.732x Current x (RcosǾ+jsinǾ) x Cable Lengthx100) / (Line Voltage x No of Runx1000)
  • Voltage Drop of Cable= (1.732x139x(0.57×0.8+0.077×0.6)x200x100)/(415x1x1000)=5.8%
  • Voltage Drop of Cable=5.8%
  • Here Voltage drop for 70 Sq.mm Cable (5.8%) is higher than Define Voltage drop (5%) so either select higher size of cable or Increase no of Cable Runs.
  • If we Select 2 No’s of Run than Voltage drop is 2.8% which is within limit (5%) but to use 2 no’s of Run of cable of 70 Sq.mm Cable is not economical so It is necessary to use next higher size of Cable.

Selection of Cable Case (2):

  • Let’s Select 3.5Core 95 Sq.mm cable for Single run, S.C Capacity =8.2KA.
  • Current Capacity of 95 Sq.mm cable is 200Amp,Resistance=0.41Ω/Km and Reactance=0.074 mho/Km
  • Total De rating Current of 70 Sq.mm Cable= 200×0.93 =187 Amp.
  • Voltage Drop of Cable= (1.732x139x(0.41×0.8+0.074×0.6)x200x100)/(415x1x1000)=2.2%
  • Voltage Drop of Cable=2.2%
  • To decide 95Sq.mm Cable, Cable selection condition should be checked.
  • (1) Cable De rating Amp (187 Amp) is higher than Full Load Current of Load (139 Amp) =O.K
  • (2) Cable Voltage Drop (2.2%) is less than Defined Voltage drop (5%) =O.K
  • (3)No of Run of Cable (1) >= (139A / 187A =0.78) =O.K
  • (4) Cable S.C Capacity (8.2KA) is higher than System S.C Capacity at that Point (6.0KA) =O.K
  • 95 Sq.mm Cable satisfied all three condition so It is advisable to use 3.5 Core 95 Sq.mm cable

Calculate Fault current at various point of Distribution system(Excel).


  • ScreenHunter_01 Jan. 29 20.10Calculate Total impedance of upper stream.
  • Calculate Total impedance of Lower stream.
  • Calculate impedance of Transformer.
  • Calculate Fault current on Secondary of Transformer.
  • Calculate minimum size of Cable to withstand Isc.
  • Calculate Fault current at various location of Distribution System.
  • Calculate Min Size of Cable at various location of Distribution System.

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