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RELAY SETTING FOR MOTOR
VOLTECH ENGINEERS PVT.LTD.
PROJECT: 2 x 150 MW COAL BASED THERMAL PROJECT, THOOTHUKKUDI
TITLE: RELAY SETTING FOR 6.6KV MOTOR
CLIENT : IND BARATH THERMAL POWER LIMITED
DATE/REV 12.06.12/0
6.6kV Unit Service Switch Board ,
1700KW ID FAN
INPUT DETAILS:-
I. CT Detailsa. CT Ratio=250/1Ab. CT Primary=250Ac. CT Secondary=1A
II. Motor Details a. Output(Pnm)=1700KWb. Rated voltage(Unm)= 6600Vc. Motor FLC(Inm) = 183.9A
d. LRC-pu = 6.5Timese. LRC-Amps =1195.0Af. Motor Starting time =5sec
g. No load Current=24Ah. No load Starting Time =5 Sec
i. Locked rotor withstand timea. Hot Start=2b. Cold start=3
j. Starting Method/Coupling=DOLIII. Relay Details
a. Relay Type = P220b. Make = ALSTOM
A. RELAY SETTING:-1) THERMAL OVER LOAD
PROTECTION(49)Note: Refer Thermal limitation, current-time curve
1.1)Threshold = Iθ Motor FLC(In)=184A
Iθ = [(FLC X1.05)/CTR]*1.2Iθ =[(183.9x1.05)/250]*1.2Iθ=0.93*In
Relay thermal overload characteristics shall be below the motor hot & cold thermal withstand characteristics. Based on the motor characteristics we have chosen.
1.2) Hot & Cold Curve Setting: a. Heating time constant as
=13b. Cooling time constant =15
Trip time characteristics t=T ln [(K^2 - θi) /(K^2-θthresh)]
where,t = operating time in secondsT = thermal time constant value in secondsIeq = equivalent thermal current valueIθ> = thermal overload current thresholdK = Ieq / Iθ> ratioθi = initial thermal state value ; (in our case θi equal to 0)θthresh = alarm threshold (settable) or tripping threshold (fixed value equal to 1)
So, above formula rewritten as,t = T ln [(K^2)/(K^2 - 1)]
a. Is Heating Time constant within safe?
i. At 500% of FLC Load current taken=500% of FLC
Trip time =0.60min(35.85sec)
ii. At 400% of FLC Load current taken= 400% of FLC Trip time =0.94min(56.51sec)
iii. At 300% of FLC Load current taken=300% of FLC Trip time =1.73min(103.74sec)
iv. At 200% of FLC Load current taken=200% of FLC Trip time =4.22min(253.00sec)
Hence the chosen Heating Time constant 13 is below the motor thermal curve (hot).
b.Is Cooling Time constant within safe? Cooling time constant =15
i. At 500% of FLC Load current taken=500% of FLC
Trip time = 0.69min(41.37sec)
ii. At 400% of FLC Load current taken= 400% of FLC
Trip Time =1.09min(65.20sec)
iii.At 300% of FLC Load current taken=300% of FLC Trip Time =1.99min(119.70sec)
iv.At 200% of FLC Load current taken=200% of FLC Trip Time =4.87min (291.92sec)
Hence the chosen cooling Time constant 15 is below the motor thermal curve (cold).
1.3Themal Alarm Threshold (θ Alarm)
= (FLC)/(Threshold Iθ)
= 183.9/194
= 0.95=95 %
1.4Forbid Start :
θforbid start < [(Id / Iθ>)2 * (1 �exp(td / Te2))] + exp (td / Te2)
Where: Id = actual start-up current, td = actual start-up time, Te2 = thermal time-constant at the
moment of start-up,
Iθ> = current threshold of thermal overload,
ttrip = time of tripping for the thermal replica protection
= θforbid start < [(Id / Iθ>)2 * (1 exp(td / Te2))] + exp (td / Te2)�
=(1195/194)^2x(1exp(10/10))+exp(10/10)
=0.69 = 69
2 SHORT CIRCUIT PROTECTION(50/51)
Motor starting current,IS =1195 A
130% of Motor Start Up current= 1553.5 A
= 1553.5*(1/250)
Current threshold I>> = 6.20In
Time-delays tl>> = 0.10 s
3 EARTH FAULT PROCTION(50/51)=
Relay rated current,In = 1 A
20% of relay rated current is considered, = 0.2*1
Current thresholds lo> = 0.2A
Time-delays tlo> 0 s
For lo>> Setting to 6% of Max. Earth fault
Current thresholds lo>> =1.2A
Time-delays tlo>> = 0.1s
4 UNBALANCE PROTECTION (46)
Threshold li> = 10% of FLC of Motor
CT Ratio
= 0.1x183.9
250
= 0.074 In
Time-delays tli> = 10 Sec
Threshold li>> = 20% of FLC of Motor
CT Ratio
= 0.2x183.9
250
= 0.147 In
5 EXCESS LONG START UP PROTECTION (48)
Threshold I start = Id= Starting Current X Motor Current In→ I Start =2*Iθ
= 1195
Here Motor start-up current is higher than 6 times the rated current so
recommended setting is 3Iθ3Iθ
* Typical settings are :
• [Istart] is equal to:
⇒ 1.5*[Iθ>] if the motor start-up current is lower than 4 times the rated current;
⇒ 2*[Iθ>] if the motor start-up current is equal to or higher than 4 times the rated current and lower than 8 times the rated current;
⇒ 3*[Iθ>] if the motor start-up current is equal to or higher than 8 times the rated current.
tIstart = 1.2xtdSec
here td is Start up time
= 6 Sec
6 BLOCKED ROTOR PROTECTION (51LR/50S)
Threshold I stall = Id= Starting Current X Motor Current In→ I Start =2*Iθ
= 1195
Here Motor start-up current is higher than 6 times the rated current so recommended setting is 3Iθ
3Iθ
Type of Motor = ID FAN
tIstall = 1.7Sec
* Typical settings are :
• [Istart] is equal to:
⇒ 1.5*[Iθ>] if the motor start-up current is lower than 4 times the rated current;
⇒ 2*[Iθ>] if the motor start-up current is equal to or higher than 4 times the rated current and lower than 8 times the
rated current;
⇒ 3*[Iθ>] if the motor start-up current is equal to or higher than 8 times the rated current.
[tIstall] is 1 to 2 s for a pump and a fan, and 5 to 10 s for a crusher. In all the cases, this setting must be lower than the withstand time for the motor with the rotor stalled.
7 LOSS OF LOAD (OR) UNDER CURRENTPROTECTION (37)
Threshold I< = No load currentIt must be higher than No load
current
CT Ratio
= 24
250
= 0.096 In
tl< = This setting depends on the load driven by the motor (often set to a few seconds).
= 3 Sec
Tinhib = " This setting depends on the load connected to the motor. If the motor is
started on load , this delay time is set to its minimal value, that is to say 0,05 s. Ifthe motor is idle-started, this delay time
is set to be slightly longer than the load increase time of the motor."
= tl<+No load Stating Time
= 8 Sec
THERMAL OVER LOAD PROTECTION(49)
Sub Menu Primary SettingSecondary Setting Setting range
Thermal overload function enabled ?Yes
Thermal inhibition on start enabled ?No
Threshold Iθ> 194 A 0.930.2 to 1.5 In by steps of 0.01 In
Ke 3 0 to 10 by steps of 1
Te1 13 1 to 180 min by steps of 1 min
Te2 10 1 to 360 min by steps of 1 min
Tr 15 1 to 999 min by steps of 1 min
Influence RTD (optionalN
θALARM enabled? Yes
Thermal alarm threshold θALARM95 Set to 100%
θ FORBID START enabled ?Y
FORBID START 69 20 to 100% by steps of 1%
SHORT CIRCUIT PROTECTION(50/51)
Sub Menu Primary SettingSecondary Setting Setting range
Short-circuit function enabled ?Yes
Threshold I>> 1195 A 6.21 to 12 In by steps of 0.1 In
tI>> 0.10 0 to 100 s by steps of 0.01 s
EARTH FAULT PROCTION(50/51)
Sub Menu Primary SettingSecondary Setting Setting range
"Earth fault function enabled ?:
threshold Io>" No
Thresholds Io> 0.20.002 to 1 Ion by steps of 0.001
tIo> 0.00 0 to 100 s by steps of 0.01 s
"Earth fault function enabled ?:
threshold Io>>" Yes
Threshold Io>> 1.200.002 to 1 Ion by steps of 0.001
tIo>> 0.10 0 to 100 s by steps of 0.01 s
UNBALANCE PROTECTION (46)
Sub Menu Primary SettingSecondary Setting Setting range
"Function Unbalance enabled ?:
threshold Ii>" Yes Alarm threshold enabled
Threshold Ii> 0.10.05 to 0.8 In by steps of 0.025 In
tli> 18 A 10 0.04 to 200 s by steps of 0.01 s
"Function Unbalance enabled ?:
threshold Ii>>" YesTripping threshold enabled
Threshold Ii>> 37 A 0.150.2 to 0.8 In by steps of 0.05 In
EXCESS LONG START UP PROTECTION (48)
Sub Menu Primary SettingSecondary Setting Setting range
"Excess long start function
enabled ?" YES
Threshold Istart 582 A 3Iθ1 to 5 Iθ by steps of 0.5 Iθ
tIstart 6 1 to 200 s by steps of 1 s
BLOCKED ROTOR PROTECTION (51LR/50S)
Sub Menu Primary SettingSecondary Setting Setting range
Block rotor function enabled ?YES
tIstall 1.70.1 à 60 s by steps of 0.1 s
"Stalled-in-run rotor function
enabled ?" YES
Threshold Istall 582 A 3Iθ1 à 5 Iθ by steps of 0,5Iθ
"Blocked-at-start rotor function
enabled ?" YES
LOSS OF LOAD (OR) UNDER CURRENTPROTECTION (37)
Sub Menu Primary SettingSecondary Setting Setting range
Loss of load function enabled ?YES
Threshold I< 24 A 0.10 0.1 to 1 In by steps of 0.01 In
tI< 3 0.2 to 100 s by steps of 0.1 s
Tinhib 8 0.05 to 300 s by steps of 0.1 s
Reference Documents:
1. Motor Data Sheet
2. Single line Diagram for 6.6kV Switch board
3. MiCOM-P220_TechnicalGuide-EN
4.MiCOM -P220 Relay cataloge
5. Motor Characterstics Curve Graphs