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Aramco Standard Electrical and Instrument Question and answers
1. What is the meant by short circuit braking current?
Ans: The rated short circuit breaking current of a circuit breaker is the highest value of short circuit current
which a circuit breaker is capable of breaking under specified condition of transient recovery voltage and power frequency voltage. Expressed in K. A. RMS at contact separation
2. What is meant by short circuit making current?
Ans: Rated Making Current = 1.8 x root 2 x rated short circuit breaking current.
= 2.5 x rated short circuit breaking current
- What is range of low voltage and medium voltage and high voltage?
Ans: Low Voltage: 110 ~ 380 VAC Medium Voltage: 489 ~13.8 KV High Voltage: 14.6 ~115 KV
4. What is the different between tar and delta connection with types of motor?
5. Star Delta connection with 3 Phase Induction Motor?
Ans: Star Delta Starter: If the starter winding is directly connected with the supply it will draw high current to reduce this high current (to control starting current) Star/Delta starter is used.
6. Why does control valve operate at IS psi?
Ans: On higher pressure the actuator sizes becomes bigger in area. The actual force produced by the actuator.
Force = Pressure x Area.
= 15 psi x Area, If Area = 15″
Force produced = 15 psi x 25 in2 = 375 pounds.
Actual force acting on a control valve = 375 pounds.
Q. What are Pressure Conversions:
1 PSI = 27.74”H2O
1Kg/cm2 = 14.223 PSI
1 Bar = 0.145 PSI
Kg/cm2 = 10000 mm of H2O
1 Bar = 1.0197 Kg/cm2
1 Kg/cm2 = 0.98 Bar
1 Torr = 1 mm of Hg
Type of Lugs: (1) Shanap Type (2)
Pin Type (3) Ring Type (4) U Type
Gland Size: ½” ¾” 1”1½” 2”
Thread Type: ET (Equal Thread), BSP
(British Standard Pitch), NPT (National Pipe Pitch).
Q. What are Electrical Voltages:
LT – (Low Tension) – 50VAC ~ 230VAC
HT – (High Tension) – 320VAC ~460VAC
MCC – (Main Control Connection) or (Motor Control Center)
PCC – Power Control Connection
Q. Equipment used for no Load Run:
Tacho Hi-Tester (Hioki Model 3403) for motor speed.
True RAS Multimeter (John Fluke Model 87V).
Infrared Thermometer (John Fluke Model 66) Using to get the Temperature of.
1. Ambient Temperature
2. Bearing Drive End
3. Winding Temperature
4. Bearing non Drive End
Vibration Meter (Monarch instrument Model Examiner 1000) Using to get the Vibration (mm/s)
Q. Motor in Two Locations:
1. Drive End (Horizontal-Vertical and Axial)
2. Non Drive End (Horizontal-Vertical and Axial)
Q. USE OF Sound Level Meter (Extech Instrument Model 407703)
Using to get the noise (dB) of motor in 3 locations:
1. Drive end.
2. Non drive end.
NB: The Duration of the no load run is 4 Hrs, Every 30mm needed to get a reading.
Q. Equipment using for testing the panel board:
Michroohmeter (Model: Programma MOM200A).
Used to test the contact resistance of bas bars, breakers etc..?
Digital Earth Tester (Model: 4105A).
Portable Double Bridge (Model: 2769).
Q. Using for winding resistance tests of voltage transformer, current transformer, etc..?
DC Dielectric Test Set (Biddle Model 220123).
Q. Used to hi pot the medium voltage cables?
Insulation Tester (Megger Model: BM11D)
Q. Used to test the insulation resistance of cables, bus bars, breakers, VT’s, ct’s, etc…?
Digital Multimeter Model: 77iii
Programma (Freja 300)
Q. Relay test unit for: (transformer management relay, feeder management relay, motor management relay, also used to test the ATS of switchgear, ammeters and voltmeters
Torque wrench (model 64-046).
Power Clamp Meter (Model: Unites 93510).
True RMS AC/DC clamp meter (Tektronix Model: DCM910)
Relay Test Unit (Programma Model Sverker 750)
Voltage injections exp: test the lock out relay Breaker
Analyzer System (Programmed Model TM1600)
Q. How to calculate the accuracy of Instrument
Accuracy = Actual Value – Measured Value/Full Span x 100