Two major documents are required for this task.
They are;
- The equipment list
- Motor power user summary.
The equipment list prepared by the mechanical and process combined group is
passed to the electrical group for action. Some equipment may not be indicated
to be either electric or gas driven on the equipment list. Such equipment are
clarified on the P&ID, where detailed information concerning every equipment is
usually provided.
Motor Power User Summary
The motor power user summary is a detailed listing of all electric driven
equipment in the equipment list. Such equipment are compiled on a separate list
termed the Motor power user summary.
Voltage Levels.
After compiling the motor power user summary, the next task is to define the
voltage levels.
All motors might not run on the same voltage. Voltage levels are defined from the
motor power user summary.
Example.
A motor power user summary contains the following loads.
500Hp pump
30Hp pump
250Hp pump.
There are 2 optional voltage levels vis 4160V and 480V. What load would be
placed on which voltage level?
Solution.
The 500Hp and the 250Hp pumps should be placed on 4160V. This is done in
order to avoid very high current which may lead to having very large feeder and
other switchgear accessories to supply the pumps.
By Bechtel standards
0-130kw pumps are placed on Low Voltage
131kw and above are placed on Medium Voltage.
NOTE : This is not fixed for all projects. On EGP3 for example, 150kw pump
were placed on Low Voltage , based on the client standards and requirements.
Load Factor
This is the ratio of the time a load is used for the total time in a day. e.g if a load
is in use for 8hrs in a day the load factor is 8/24 = 1/3
Load factor = Absorbed load.
Nameplate rating
Absorbed load = Load Factor X Nameplate Rating
Absorbed load. = Efficiency
Consumed load
Consumed load = Absorbed load
Efficiency
Consumed load = Load factor X Nameplate Rating
Efficiency.
From the above, if the absorbed load is given from the equipment list the
consumed load could be calculated.
The consumed load could also be calculated from the name plate rating of the
motor using the load factor and the efficiency.
When efficiency is not given , a typical manufacturer’s reference could be
assumed.
a copy of the relevant page should be attached. Consumed load is sometimes
referred to as operating load.
The load summary can now be drawn in tabular form as shown below.
EQUIPMENT CONSUMED LOAD
TAG.
NO
|
DESCRIPTION
OF
SERVICE
|
DUTY
|
N.R
|
L.F
|
EFFICIENCY
|
CONSUMED
LOAD
|
|||
What the
equipment
would do.
|
Continuous
Intermittent
Or
Stand
by
|
KW
|
KVA
|
KVAr
|
|||||
TOTAL
|
|
||||||||
From the total on the load list, the overall power factor of the system can bedetermined.
Correction Factors.
Correction factors applied in summing the total consumed load vary from one
organization to the other.
However for the purpose of the training the following correction factors are
recommended.
Correction load (C) 100%
Intermittent load (I) 30%
Standby load (S) 0% unless otherwise stated by client e.g. Shell DEP
recommends 10% for standby loads.
From the above factors
Running load = C+ 30%I
Peak load = C + I
