Calculate Size of Contactor, Fuse, C.B, O/L of DOL Starter
- Calculate Size of each Part of DOL starter for The System Voltage 415V ,5HP Three Phase House hold Application Induction Motor ,Code A, Motor efficiency 80%,Motor RPM 750 ,Power Factor 0.8 , Overload Relay of Starter is Put before Motor.
Basic Calculation of Motor Torque & Current:
- Motor Rated Torque (Full Load Torque) =5252xHPxRPM
- Motor Rated Torque (Full Load Torque) =5252x5x750=35 lb-ft.
- Motor Rated Torque (Full Load Torque) =9500xKWxRPM
- Motor Rated Torque (Full Load Torque) =9500x(5×0.746)x750 =47 Nm
- If Motor Capacity is less than 30 KW than Motor Starting Torque is 3xMotor Full Load Current or 2X Motor Full Load Current.
- Motor Starting Torque=3xMotor Full Load Current.
- Motor Starting Torque==3×47=142Nm.
- Motor Lock Rotor Current =1000xHPx figure from below Chart/1.732×415
Locked Rotor Current
| ||
Code
|
Min
|
Max
|
A
|
1
|
3.14
|
B
|
3.15
|
3.54
|
C
|
3.55
|
3.99
|
D
|
4
|
4.49
|
E
|
4.5
|
4.99
|
F
|
5
|
2.59
|
G
|
2.6
|
6.29
|
H
|
6.3
|
7.09
|
I
|
7.1
|
7.99
|
K
|
8
|
8.99
|
L
|
9
|
9.99
|
M
|
10
|
11.19
|
N
|
11.2
|
12.49
|
P
|
12.5
|
13.99
|
R
|
14
|
15.99
|
S
|
16
|
17.99
|
T
|
18
|
19.99
|
U
|
20
|
22.39
|
V
|
22.4
| |
- As per above chart Minimum Locked Rotor Current =1000x5x1/1.732×415=7 Amp
- Maximum Locked Rotor Current =1000x5x3.14/1.732×415=22 Amp.
- Motor Full Load Current (Line) =KWx1000/1.732×415
- Motor Full Load Current (Line) = (5×0.746)x1000/1.732×415=6 Amp.
- Motor Full Load Current (Phase)=Motor Full Load Current (Line)/1.732
- Motor Full Load Current (Phase)==6/1.732=4Amp
- Motor Starting Current =6 to 7xFull Load Current.
- Motor Starting Current (Line)=7×6=45 Amp
(1) Size of Fuse:
Fuse as per NEC 430-52
| ||
| Type of Motor | Time Delay Fuse | Non-Time Delay Fuse |
Single Phase
|
300%
|
175%
|
3 Phase
|
300%
|
175%
|
Synchronous
|
300%
|
175%
|
Wound Rotor
|
150%
|
150%
|
Direct Current
|
150%
|
150%
|
- Maximum Size of Time Delay Fuse =300% x Full Load Line Current.
- Maximum Size of Time Delay Fuse =300%x6= 19 Amp.
- Maximum Size of Non Time Delay Fuse =1.75% x Full Load Line Current.
- Maximum Size of Non Time Delay Fuse=1.75%6=11 Amp.
(2) Size of Circuit Breaker:
Circuit Breaker as per NEC 430-52
| ||
| Type of Motor | Instantaneous Trip | Inverse Time |
Single Phase
|
800%
|
250%
|
3 Phase
|
800%
|
250%
|
Synchronous
|
800%
|
250%
|
Wound Rotor
|
800%
|
150%
|
Direct Current
|
200%
|
150%
|
- Maximum Size of Instantaneous Trip Circuit Breaker =800% x Full Load Line Current.
- Maximum Size of Instantaneous Trip Circuit Breaker =800%x6= 52 Amp.
- Maximum Size of Inverse Trip Circuit Breaker =250% x Full Load Line Current.
- Maximum Size of Inverse Trip Circuit Breaker =250%x6= 16 Amp.
(3) Thermal over Load Relay:
- Thermal over Load Relay (Phase):
- Min Thermal Over Load Relay setting =70%xFull Load Current(Phase)
- Min Thermal Over Load Relay setting =70%x4= 3 Amp
- Max Thermal Over Load Relay setting =120%xFull Load Current(Phase)
- Max Thermal Over Load Relay setting =120%x4= 4 Amp
- Thermal over Load Relay (Phase):
- Thermal over Load Relay setting =100%xFull Load Current (Line).
- Thermal over Load Relay setting =100%x6= 6 Amp
(4) Size and Type of Contactor:
Application
|
Contactor
|
Making Cap
|
| Non-Inductive or Slightly Inductive ,Resistive Load |
AC1
|
1.5
|
| Slip Ring Motor |
AC2
|
4
|
| Squirrel Cage Motor |
AC3
|
10
|
| Rapid Start / Stop |
AC4
|
12
|
| Switching of Electrical Discharge Lamp |
AC5a
|
3
|
| Switching of Electrical Incandescent Lamp |
AC5b
|
1.5
|
| Switching of Transformer |
AC6a
|
12
|
| Switching of Capacitor Bank |
AC6b
|
12
|
| Slightly Inductive Load in Household or same type load |
AC7a
|
1.5
|
| Motor Load in Household Application |
AC7b
|
8
|
| Hermetic refrigerant Compressor Motor with Manual O/L Reset |
AC8a
|
6
|
| Hermetic refrigerant Compressor Motor with Auto O/L Reset |
AC8b
|
6
|
| Control of Restive & Solid State Load with opto coupler Isolation |
AC12
|
6
|
| Control of Restive Load and Solid State with T/C Isolation |
AC13
|
10
|
| Control of Small Electro Magnetic Load ( <72VA) |
AC14
|
6
|
| Control of Small Electro Magnetic Load ( >72VA) |
AC15
|
10
|
- As per above Chart
- Type of Contactor= AC7b
- Size of Main Contactor = 100%X Full Load Current (Line).
- Size of Main Contactor =100%x6 = 6 Amp.
- Making/Breaking Capacity of Contactor= Value above Chart x Full Load Current (Line).
- Making/Breaking Capacity of Contactor=8×6= 52 Amp.
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