SAI-348D digital motor protection and control device

I. Overview
SAI-348D digital backup motor protection devices for 10kV and below the voltage level of the various system wiring ( ungrounded system , a small current grounding system ) integrated protection in high voltage asynchronous motors, asynchronous motors as a medium to large (hundreds kilowatts or more ) internal fault , overload protection , etc. . Can be installed in the switch cabinet in place , but also set the screen installed in the control room.
Protection configuration
● reflect the speed off phase fault protection
● reflect Stall overcurrent protection
● Overload protection ( alarm , trip )
● Start time is too long to protect
● unbalance protection ( including off -inverting and inverting ) : definite time or inverse time negative sequence overcurrent protection
● Thermal protection ( overheat trip , overheating alarm , heat accumulation memory function )
● Low Voltage Protection
● Over Voltage Protection
● non-power protection
● ground protection ( zero sequence overcurrent protection can trip or signal tuning , selectable definite time or inverse time )
● F-C overcurrent latch
Control Function Deployment
● function with SAI-318D.

Second, the principle that the protection of
2.1 Start-up time is too long to protect
Means for measuring motor starting time Tstart method : When the maximum phase current of the motor from zero mutation move 10% Ie start counting until after excessive peak starting current drops to 120% Ie when the last date, is called the Tstart. (Ie is the motor rated current. ) Motor starting time is too long will cause the rotor to overheat, start-up time when the actual measurement device exceeds the allowable start time setting Tstart, protective action on the trip .

2.2 , instantaneous protection
Instantaneous protection by determining the size of the current to achieve, its tuning range (3 ~ 12) Is. Quick break down automatically to protect the motor starting after half finished . That would effectively escape the huge start-up current of the motor, and can guarantee to provide preparedness severe overload caused by the normal starting motor stall protection .
Action time T1 can tuning circuit breakers for motor control tuning time is usually shorter , and time spent tuning the motor contactor control generally longer, choose the setting of 0.3 seconds.
Its action logic is as follows :

Where Ia, Ib, Ic is the phase current , Isn breaking current value for the speed
2.3 , overcurrent
The overcurrent protection device settings , when the current is greater than the current setting and reaches the setting time, overcurrent exports.
Overcurrent protection automatically exit when the motor is started automatically put into the starting end .

2.4 , overload protection
The overload protection device settings , when the current is greater than the current setting and reaches the setting time via the control word to select an alarm or trip . Overload protection automatically exit when the motor starts automatically put into the starting end .

Where Ia, Ib, Ic is a phase current , In the overload value
2.5 , overheating protection
Considering the motor is positive, the thermal effect generated by the negative sequence current , the motor load caused by superheating of various protection , short-circuit and as a motor start-up time is too long, such as back- stall .
Equivalent current Ieq to simulate the heating effect of the motor , namely:

Where : Ieq- equivalent current
I1- positive sequence current
I2- negative sequence current
K1- positive sequence current heat coefficient , the motor during startup K1 = 0.5, start the restoration is completed K1 = 1
K2- negative sequence current heat coefficient , K2 = 3 ~ 10, desirable K2 = 6
According to the heating characteristic curve of the motor model , the operation of the motor operating current and the equivalent time t between Ieq is given by the following equation :

Where: Ip- load current before overload if the overload is cold front , then Ip = 0
I ∞ - starting current , that protection is not required for operation of the provisions of the current limit
the time constant τ- reflecting capacity of the motor overload
This criterion is fully considered the motor stator and thermal process state before the load is too hot . Device to indicate the heat content of the motor is proportional to the square of the heat , the heat content of the stator current , by conversion, into its dimensionless motor overload capacity reflects the time constant τ. When the heat content value reaches τ, the device is tripped . When the heat content of Ka × τ, hair overheat alarm signal , which , Ka is a warning factor , which ranges : thermal alarm can be set to heat accumulation whole trip ( 60 to 99.9 ) % , the device provides real-time heat accumulation value display , alarm indication lights and signal contacts output.
According to the principle of the motor can be started twice in a row , each time you start the trip 50% of its value should not be greater than the heat accumulation , so when the heat accumulation value drops below 50 percent , closing latching device contacts to return. After tripping overtemperature protection , thermal memory device startup , output contacts have been closed until the heat accumulation value drops below 50 percent , closing latching contacts overheating return , then the motor can be restarted. When an emergency situation requiring immediate start, thermal reversion operation of the device .
Starting current I ∞ rated current Ie can be 1.05 to 1.15 times the setting .
Thermal time constant τ provided by the electrical plant , if the manufacturer does not provide , according to the estimate of one of the following methods :
① If manufacturers provide thermal limit curve or a group of motor load capacity over the data , then calculated as τ:

After obtaining a set of τ small value .
② if known Stall current I and allowed to stall time t, but also by the following formula to estimate τ:

③ calculated as τ:

Where : θe rated motor temperature , K is the starting current multiples , θ0 ​​is the temperature rise of the motor startup , Tstart as motor starting time .
Its action logic is as follows :

2.6 , zero sequence overcurrent protection
Ground current depends on the motor power system grounding. In ungrounded or high resistance grounded system , the fault current is only a few amperes , resistance grounding system in hundreds of amperes , direct grounding system will be greater in value . For a high level of ground fault current system , if the three-phase current transformers are equipped with zero- sequence current three-phase currents can be achieved . In most cases , in order to detect low ground current , zero sequence current transformer is often necessary to obtain a zero-sequence current. Thus , microprocessor-based motor protection designed for both two-phase current transformer with zero sequence current transformer plus the way , three-phase current transformer can also be a way .
Its action logic is as follows :

Where I0 zero sequence current , I0d zero sequence current value
2.7 , negative sequence overcurrent
The main negative sequence current protection for a variety of non-ground asymmetry fault , motor inverter , phase , and a more serious turn short circuit between the electrical
Provide protection pressure asymmetry abnormal operating conditions. When the motor phase currents greater asymmetry, a larger negative sequence current and the negative sequence current will generate twice the power frequency current in the rotor , the rotor is attached fever greatly increased , endangering the safe operation of the motor. When the motor is running , due to the asymmetric power supply , there is always a certain degree of negative sequence current, which will not exceed 30% Is, negative sequence protection tuning should be able to escape this negative sequence current , ie 0.3Is tuning . Operation time characteristics selectable two -time characteristics , select definite time and inverse, extremely inverse action equation:

Where : tp is the time factor , the range of ( 0.05 to 1 )
Ip is the negative sequence current setting
I fault negative sequence current
t for the trip time
Note: The setting value multiplied by the value of inverse time as part of the molecules in the above expression , in seconds , tuning range ( 0.4 to 80 ) .
Its action logic is as follows :

Which is negative sequence current I2 , I2d negative sequence current value
2.8 , low voltage protection
In order to ensure the safety of production, does not allow self-starting motor , the power supply voltage disappears or is reduced, low- voltage protection on the trip , the motor is automatically disconnected from the grid . When three line voltage is below a given value, the switch or contactor in the closed position , and the A, the C -phase current is zero, low- voltage protection . PT cut to prevent motor burnout mistake , when single-phase or two-phase PT break in the negative -sequence voltage , the device through the negative sequence voltage ( internal threshold 8V) automatic locking low- voltage protection.
Its action logic is as follows :

2.9 , over- voltage protection
Power overvoltage causes iron loss and copper loss is increased, the temperature rise of the motor . When any phase voltage is greater than the tuning voltage , protection by tuning delay action .
2.10 , non-power protection
Come from non-electric motor body contact, to switch the device input terminals , the trip or not is determined by the soft platen. Such as soft platen exit , only for ordinary credit away , otherwise it will jump all the switches accordingly . After the device trips, event logging , and MMI will be recorded by the computer to upload to the background .
2.11, F-C overcurrent latch
For fuse - high voltage contactor (FC) to control the motor if either one of the phase fault current exceeds the current interrupter contacts to protect the outlet is blocked, the contactors can not be disconnected at this time, to the removal of the fuse is blown by failure.
When the motor phase current mutation is zero , the voltage is normal and contacts send alarm signals blown fuse together bit .
2.12 PT disconnection detection
Function with SAI-318D.
PT disconnection detection function can be cast back through the control word.
2.13 Data Records
Function with SAI-318D.
2.14 , remote telemetry, remote control
Function with SAI-318D.

Three: device tuning information
3.1 , setting the value of a list and description of
No. Name Symbol Range Unit Remarks
A control word KG1 0000 ~ FFFF no see control word description
2 rated motor current Ie 0.5 ~ 20.0 A
3 motor starting time Tstart 1 ~ 20S S
4-speed breaking current value Isd 0.2 ~ 100.0 A
5-speed off time Tsd 0.0 ~ 20.00 S
6 overcurrent settings Igl 0.2 ~ 100.0 A
7 overcurrent time Tgl 0.2 ~ 3000 S
8 overload setpoint Igfh 0.2 ~ 100.0 A
9 overload time Tgfh 0.2 ~ 3000 S
10 zero-sequence current value I0 0.04 ~ 5.00 A
11 zero-sequence current time T0 0.0 ~ 20.00 S
10 Negative sequence current value I2 0.2 ~ 100.0 A
12 negative-sequence definite time T2 0.1 ~ 20.00 S
13 negative-sequence inverse time T2fsx 0.4 ~ 80 S uses extremely inverse
14 low voltage setpoint Udy 2.0 ~ 100.0 V line voltage
15 Low voltage operation time Tdy 0.0 ~ 20.0 S
16 over-voltage setpoint Ugy 2.0 ~ 100.0 V -phase voltage
17 Low voltage operation time Tgy 0.0 ~ 20.0 S
18 overheating starting current I ∞ 0.2 ~ 20 A
19 thermal time constant τ 6 ~ 3000 S
20 coefficients of thermal effect of negative sequence current K2 3 ~ 10 generally advisable to 6
21 overheat alarm coefficient Krgj 0.3 ~ 1.0 is generally taken as 70%
Cooling time of 22 multiple Ksr 1 ~ 5 times τ multiple of 4.0 is generally desirable
23 non-power a delay Tfdl1 0.0 ~ 100.0 S
24 non-power two delay Tfdl2 0.0 ~ 100.0 S
25 non-power 3 delay Tfdl3 0.0 ~ 100.0 S

Meaning Bit 0 is set to 1 when the meaning set
15 CT rated current of 1A CT rated current of 5A
14 into motor starter motor starter discrimination discrimination exit
10 to 13 Reserved Reserved
9 overload tripping overload alarm
8 Reserved Reserved
7 -phase current of two -phase to three-phase phase current CT CT
6 Reserved Reserved
5 PT break into PT disconnection discriminating judgment exit
4 control back into the control back to the disconnection disconnection discriminating judgment exit
3 Negative sequence overcurrent inverse time mode selected negative sequence overcurrent time mode is selected
2 zero- sequence protection vote cast zero sequence protection trip alarms
An overheated latch into latching exit overheating
0 overheat alarm inputs overheat alarm exit
3.2 , soft list and description of the platen
Corresponding function name plate
Current speed off current protection feature cast back
Overcurrent overcurrent protection cast back
Ground protective grounding protection cast back
Negative sequence overcurrent cast back negative sequence overcurrent protection
Overheat protection thermal protection cast back
Low voltage and low voltage protection cast back
Over-voltage over-voltage protection cast back
Overload protection Overload feature cast back
Non-electricity a non-power cast a trip back
Non-power consumption 2 2 Non- tripping cast back
Non-power consumption 3 3 Non- tripping cast back