VSD Current Overload Protection
VSDs include standard Overload protection for both the Motor and Inverter (VSD). The Overload Capacity for the Inverter is noted in the technical manual as follows (Overload Capacity):
- G type:150% rated current 60s; 180% rated current 3s.
- P type: 120% rated current 60s;150% rated current 3s.
These ratings are however only indicating 2 points on the Inverter Current Overload Curve illustrated as follows:
If any of the above scenarios occur, the VSD will stop with the following Error Code:
- Err10: Frequency Inverter Overload (this means the load current exceeds the Inverter’s current limits based on the Inverter Current Overload Curve)
Like the Inverter Current Overload protection, the VSD also protects the Motor against Current Overload. This is based on a similar (but different) curve as used for the Inverter Overload but ignores the Inverter Current Rating and instead use the Motor Rated Current as set by using parameter d0-02 (which would typically be set somewhat lower than the Inverter current rating). The Motor Current Overload Curve is illustrated as follows:
If any of the above scenarios occur, the VSD will stop with the following Error Code:
- Err11: Motor Overload (this means the load current exceeds the Motor’s Current limits based on the Motor Current Overload Curve)
By default, the VSD will Free Stop the motor when Err11 occurs, but this can be changed using parameter bb-32 which allows options to rather stop the motor according to the set stop mode or to continue running.
For additional Motor Protection the following settings can be set to limit load current (this basically allows for another overcurrent point – over and above the Motor Overload Protection Curve points):
- bd-00 (Overset Alarm Current Value): Use this to specify the Current Limit (Amps).
- bd-01(Overcurrent Alarm Delay Time): Use this to specify the Time Delay (Seconds) to allow for.
For example: If a 4KW inverter rated current is 9A but the requirement is to protect the motor when the load current reaches 6A for more than 5s, Set: bd-00 = 6 and bd-01=5. If the load current exceeds this specified current and time limit, an Err24 protection error will be displayed and the VSD will stop.
Other related Current Overload Errors that might occur includes the following:
- Err02: Over Current During Acceleration
- Err03: Over Current During Deceleration
- Err04: Over Current at Constant Speed
Err02, 03 or 04 are built-in hardware circuit protection faults (please refer to the manual for more details regarding possible causes and solutions.
For Early Warnings on possible overloads, the VSD Relays and Digital Outputs can also be used to set up triggers/warnings using some of the following Functions:
- Function = 22 (Current 1 Reached): This function can be used as trigger indicating whether the load current falls within a set range, using b4-35 as a set point and b4-36 (Amplitude of any current reaching 1) to indicate the allowed range (variance).
- Function = 23 (Current 2 Reached): This function (same as Function = 22) can be used as trigger indicating whether the load current falls within a set range, using b4-37 as a set point and b4-38 (Amplitude of any current reaching 2) to indicate the allowed range (variance).
If the output current of the VSD is within the positive and negative amplitudes of any current reaching detection value, the corresponding DO becomes ON.
- Function = 27 (Output Current Exceeded Limitation): If the output (load) current of the VSD is equal to or higher than the over current threshold (b4-33 = Over current output threshold) and the duration exceeds the detection delay time (b4-34 = Over current output detection delay time), the corresponding DO becomes ON. Note that these parameters do not influence the motor overload current curve, its merely used as an early warning function.
- Function = 29 (Frequency Inverter Overload Pre-Warning): The VSD judges whether the load exceeds the Inverter overload pre-warning threshold before performing the protection action. If the pre-warning threshold is exceeded, the terminal becomes ON. This pre-warning is based on the inverter overload curve, but with a duration of 10 seconds less than used for the actual Overload Error (Err10).
- Function = 31 (Motor Overload Pre-Warning) – the VSD judges Motor overload according to the motor overload threshold, and terminal becomes ON. The pre-warning coefficient can be adjusted using parameter bb-03 (default = 80%). bb-03 is used to give a warning signal to the control system via DO before motor overload protection occurs. This parameter is used to determine the percentage at which the pre-warning is performed before motor overload protection occurs. The larger the value is, the less advance the pre-warning will be. When the output current of the VSD is greater than the value of the overload inverse time-lag curve multiplied by bb-03, the DO terminal of the VSD set with motor overload pre-warning becomes ON. Note that the value of bb-02 also influence the value used for this pre-warning. Pre-Warning threshold = 220% × bb-02 × rated motor current x bb-03. If the load reaches this value, the VSD reports motor overload pre-warning.
Please Note: For Smaller Drives with only one set of Relays (TA-TB-TC), use the TA2-TB2-TC2 Relay parameter settings.
Adjusting the Inverter Overload Protection Curve:
- Adjust bb-39 (Inverter Overload Protection Gain)
* It is generally not recommended to change this.
Adjusting the Motor Overload Protection Curve:
- Adjust bb-02 (Motor Overload Protection Gain)
* It is generally not recommended to change this.
For the above 2 settings the VSD determines whether the Inverter or Motor is overloaded according to the inverse time-lag curve of the Inverter or Motor overload protection. The inverse time-lag curve of the Inverter or Motor overload protection is:
- For Inverter: 115% × (bb-39) × rated inverter current (if the load remains at this value for one minute, the VSD reports inverter overload fault), or 160% × (bb-39) × rated inverter current (if the load remains at this value for 20 seconds, the VSD reports inverter overload fault).
- For Motor: 225% × (bb-02) × rated motor current (if the load remains at this value for 30 seconds, the VSD reports motor overload fault), or 115% × (bb-02) × rated motor current (if the load remains at this value for 80 minutes, the VSD reports motor overload fault).
It is generally not recommended to change bb-39 or bb-02:
- If the value of bb-02 is set too large, it may damage the motor because the motor overheats but the VSD do no report an error alarm.
- If the value of bb-39 is set too large, it may damage the inverter because the load is more than what the internal circuitry is designed for and the VSD do not report an error alarm.
Disabling the Motor Overload Protection:
Although not advised, this can be done by setting bb-01 =0 (Motor overload protection Disabled)
This means the motor is exposed to potential damage due to overheating. A thermal relay is suggested to be installed between the frequency inverter and the motor.
* It is generally not recommended to change this.
