1) Motor starting analysis are generally performed for the largest motor connected to a switchboard. 2) For worst case results, motor starting analysis are generally performed considering the weakest source. 3) Considering the above two facts, any given electrical network, where a starting analysis of a motor is required, can be reduced to a simplified network consisting of a source (generator/s or grid), the starting motor (largest motor), the running motor/s (second largest motor/s or motor of same rating as the largest motor under study) and other loads lumped together. 4) Modeling This spread sheet allows the user to model a given network as follows: a) Generator/s: The details of one generator shall be entered. If there are more than one generator of identical rating, these can be modeled simply by enter the number of generator in parallel. b) Grid: The details of grid shall be entered c) Transformer/s: The details of one transformer shall be entered. If there are more than one transformer of identical rating, these can be modeled simply by enter the number of transformer in parallel. d) The spread sheet considered either the "Generator/s" or the "Grid" supply for the motor starting analysis. The "source for the motor starting analysis" can be selected by the use via the drop down menu. The selection automatically simulates switching "ON" or "OFF" the respective source breaker. e) Starting Motor: The details of the largest motor connected to the switchboard shall be entered. f) Running Motor/s: The details of the second largest running motor/s (or motor of rating same as the starting motor) connected to the switchboard shall be entered. This model can also be utilized by the user to check the voltage drop at the terminals of any remote motor/s. g) Lumped Load: The details of the remaing load on the switchboard can be modeled as a lumped load. The % motor can be defined which shall be modeled as constant power load while remaining % of load shall be modeled as constant impedance load for the calculation. h) Error in data entry of the "voltage" input shall be highlighted, if bus voltages are much different from the generator terminal voltage input of transformer voltage ratio inputs. 5) Calculation: The spread sheet performs a static motor starting analysis using the iterative method. The re-acceleration of motors is not considered. Ensure that the following options are enabled: Tools=>Options=> Calculation=> Automatic=> Iteration=>Max iteration= 100=> Max change = 0.001 Note: Change of any variable in the spread sheet, automatically initiates the iteration and recalculated the results. It may happen that due to incorrect details, the iteration diverges and erroneous results are displayed. In such case, check and correct the input and press "Ctrl+Shift+H" to reset. 6) Results: Two sets are of results are displayed on the spread sheet as follows: Prestart: These voltages and power flows results are for "Pre-start" condition. i.e. before the starting of the "Starting motor" During: These voltages and power flows results are for "Starting" condition. i.e. at the time of starting of the "Starting motor" Sr. No. Notes
IntroductionSr. No.Notes1)Motor starting analysis are generally
performed for the largest motor connected to a switchboard.2)For
worst case results, motor starting analysis are generally performed
considering the weakest source.3)Considering the above two facts,
any given electrical network, where a starting analysis of a motor
is required, can be reduced to a simplified network consisting of a
source (generator/s or grid), the starting motor (largest motor),
the running motor/s (second largest motor/s or motor of same rating
as the largest motor under study) and other loads lumped
together.4)ModelingThis spread sheet allows the user to model a
given network as follows:a)Generator/s: The details of one
generator shall be entered. If there are more than one generator of
identical rating, these can be modeled simply by enter the number
of generator in parallel.b)Grid: The details of grid shall be
enteredc)Transformer/s: The details of one transformer shall be
entered. If there are more than one transformer of identical
rating, these can be modeled simply by enter the number of
transformer in parallel.d)The spread sheet considered either the
"Generator/s" or the "Grid" supply for the motor starting analysis.
The "source for the motor starting analysis" can be selected by the
use via the drop down menu. The selection automatically simulates
switching "ON" or "OFF" the respective source breaker.e)Starting
Motor: The details of the largest motor connected to the
switchboard shall be entered.f)Running Motor/s: The details of the
second largest running motor/s (or motor of rating same as the
starting motor) connected to the switchboard shall be entered. This
model can also be utilized by the user to check the voltage drop at
the terminals of any remote motor/s.g)Lumped Load: The details of
the remaing load on the switchboard can be modeled as a lumped
load. The % motor can be defined which shall be modeled as constant
power load while remaining % of load shall be modeled as constant
impedance load for the calculation.h)Error in data entry of the
"voltage" input shall be highlighted, if bus voltages are much
different from the generator terminal voltage input of transformer
voltage ratio inputs.5)Calculation: The spread sheet performs a
static motor starting analysis using the iterative method. The
re-acceleration of motors is not considered.Ensure that the
following options are enabled:Tools=>Options=>
Calculation=> Automatic=> Iteration=>Max iteration=
100=> Max change = 0.001Note: Change of any variable in the
spread sheet, automatically initiates the iteration and
recalculated the results. It may happen that due to incorrect
details, the iteration diverges and erroneous results are
displayed. In such case, check and correct the input and press
"Ctrl+Shift+H" to reset.6)Results: Two sets are of results are
displayed on the spread sheet as follows:Prestart: These voltages
and power flows results are for "Pre-start" condition. i.e. before
the starting of the "Starting motor"During: These voltages and
power flows results are for "Starting" condition. i.e. at the time
of starting of the "Starting motor"The voltage variations shall be
highlighted if they exceed the permissible limitsAlso power flow
over the cable-1 shall be highlighted if it exceeds the generator
capacity7)Application: This spread sheet can be useful for
following checksa)Accessing normal running and starting voltage
dropsb)Deciding the number/rating of the generator for starting a
given rating of largest motorc)Checking adequacy of selected cable
sizes etc.
CalculationNotesGridFault
MVAkVX/RGridZ1ohmsGridR1ohmsGridX1ohmsE=100.000%3-ph1)The spread
sheet cells highlighted asare for userdata
entry.1006120.360000.029900.358762)Following voltage variation is
permissible:SOURCE FOR STATIC MOTOR STARTING ANALYSIS =GENERATOR
ONLY100.00MinMaxDuring normal operation:95%105%Prestart0.000
MW0.000 MVarApf0.01.000During motor starting condition:80%115%3)The
static motor starting analysis allows user to select either the
generator/s or grid supply as source. (Weak source should be
considered for worst case results).During0.000 MW0.000
MVar0.01.000Set Grid Terminal voltage =100.0%4)The spread sheet
allows more than one number of transformer /generator / motor of
identical rating to be modeled in parallel. The load flow result
indicated on the branch side are for single
circuit.Vt-prestart100.00%Bus-3 Voltage =6.000
kVVt-duringstart100.00%5)Voltages and power flows for "pre-start"
condition, i.e. before starting of the motor are displayed in
"black" font.4.50.36)Voltages and power flows for "during-start"
condition, i.e. at the time of starting of the motor are displayed
in "blue" font.Transformer/s7.50.5Nos. of Transformers in
parallel=1X'merMVAX'merprikVX'merseckVX'merImp -
Z1(pu)X'merX/RX'merZ1ohmsX'merR1ohmsX'merX1ohmsNos. of Generator
circuits in
parallel=12.560.40.06010.670.003840.000360.00382E=116.2%Vt-prestart100.0%0.30.060Generator/sVt-duringstart100.00%0.5R0.0016GMVAkVpf(pu)Xd"(pu)Xd'(pu)Xd"/RXs(pu)QmaxMvarSet
Generator Terminal voltage =100.0%Bus-1 Voltage =0.400
kV10.40.80.200.28201.550.8350.80ApfVt-prestart100.00%0.200.04480.248Prestart0.000
MW0.000 MVar0.01.000Vt-duringstart89.43%ApfPrestart0.779 MW0.480
MVarCable-1 : size3C300During0.000 MW0.000
MW0.01.0000.921320.90.851r(ohms/km)x(ohms/km)Nos of
runslength(km)1.131828.10.767During0.869 MW0.727
MVar0.12700.078030.1ONOFFMWMvarpfAmpBus-2
Voltage=0.400kVPrestart0.7570.4660.8511320.9Vt-prestart97.16%97.16%98.66%During0.8260.7010.7631828.145272316Vt-duringstart85.54%85.54%97.80%ONONONCable-2
: size3C185Cable-3 : size3C185Cable-4 :
size3C185r(ohms/km)x(ohms/km)Nos of
runslength(km)r(ohms/km)x(ohms/km)Nos of
runslength(km)r(ohms/km)x(ohms/km)Nos of
runslength(km)Prestart0.000 MW0.000 MVarPrestart0.690 MW0.425
MVarPrestart0.067 MW0.042
MVar0.12700.078010.10.12800.075010.150.12800.075020.15During0.082
MW0.243 MVarDuring0.677 MW0.416 MVarDuring0.067 MW0.042
MVarVt-prestart97.16%Bus-4 Voltage =0.400 kVVt-prestart85.56%Bus-5
Voltage =0.400 kVVt-prestart96.59%Bus-6 Voltage =0.400
kVVt-duringstart83.41%MWkVpf(pu)eff(pu)LRC(pu)LRC
pf(pu)Vt-duringstart72.63%MWkVpf (pu)%
MotorVt-duringstart84.90%MWkVpf(pu)eff(pu)REVISION-1MMNos. of Motor
circuits=1Prepared
By0.0450.40.750.754.50.30.650.40.8575%0.050.40.850.75Starting
MotorRunning Motor/sFLC Amp115.47433.41Lumped LoadFLC
Amp1203.61340.3FLC [email protected]
HK: Set generator terminal voltage in % of generator rated
voltage depending on its AVR regulation (95% to 105%). Minimum
generator terminal voltage shall be considered for worst case
resultsHK: Enter number of identical generator circuits (i.e.
Generator and its associated 'Cable-1') in parallel at 'Bus-2'.HK:
Enter number of identical Transformers in parallel at 'Bus-2' and
'Bus-3'.HK: Enter number of identical Motor circuits (i.e. Motor
and its associated 'Cable-4'), in parallel at 'Bus-3'.HK: Set grid
terminal voltage in % of grid rated voltage depending on min/max
bus voltage variation observed (95% to 105%). Minimum grid terminal
voltage shall be considered for worst case
[email protected]
