ELECTRICAL OVERLOAD
Overload as name reflects; Defines the excess level more than the capacity. Similarly, In Electrical, Overload defines excess current flow more than the rated capacity !
To derive any type of electrical load, it should be connected with the rated voltage supply. Then, it consumes current according to its capacity.
Voltage remains the same across different types of loads. Yet, the level of current depends on the power rating of the load.
That’s why back-end fuses and power cables are designed according to the rated current. Cables are also designed by considering the fault current situations.
A name plate of VFD 2.2 KW 3 phase 400 VAC is shown above. It has an input voltage range of 342-528 Volts. The input frequency range is 48-63 Hz. The current rating is 6.2 Amps.
Output AC voltage range is 0-460 VAC. Output frequency range is 0-400 Hz. Continuous output current rating is 6 Amps While overload current rating is 9 Amps for up to 60 Sec.
GIF EXPLANATION OF OVERLOAD
A GIF below shows the overload phenomenon occurring on Electrical Motor. An Electrical Motor has a current rating of 2 Amps. It is connected with a rated supply of 230V AC. This setup uses a 2 pole 6 Amps MCB. CT coil is placed on one of the wire; To measure the Electrical Current.
At initial state, MCB is available in off position. When MCB get shifted to ON, Power supply get available to electrical Motor Which results motor starts rotating. Ampere meters shows the current reading of 2 Amps.
When an external heavy load is applied on the motor. Motor’s intake current goes on increasing from 2,3,4,5 & at last 7. At 7Amps, MCB get trip.
Below 6 Amps motor works fine. But when ampere exceed the rating of 6 Amps, At 7 Amps MCB get trips.
MCB actually follows the inverse time characteristics. Which means higher the fault current leads to lesser tripping time !
REASONS OF OVERLOAD
There are multiple reasons of overload, Some of them are discussed ahead. Some overload conditions appears rapidly while some overload conditions get increased over the time.
- OVERLOAD DUE DAMAGED BEARING OR BUSHES
- OVERLOAD DUE TO LACK OF GREASE OR LUBRICATION
- OVERLOAD DUE TO EXCESS MECHANICAL LOADING
- WRONG CONNECTIONS
Motors are designed to operate at rated voltage with the correct winding configuration. Otherwise, the motor’s intake current can surpasses the rated current. This situation will create an overload-like condition.
OUTCOMES OF OVERLOAD
If compare with short circuit, Overload is a long term phenomenon. Outcomes of overload are not instant. However, it deteriorates the condition. This reduces the useful life of the system. Next, Some of the outcomes of overload been discussed.
- Degraded useful life
Overload exerts; excess burden on the system which results reduction in useful life. Due to excess burden wear & tear increases.
Here we are taking an example of Electrical Motor. When burden falls on Electrical motor, Due to extra line current, Winding get heated up. Which results winding insulation deteriorates.
Bearings or bushes also get heated up. The grease inside the bearing starts melting and escapes from the inner shells of bearings or bushes. Which results bearings or bushes get dry & their sizes get damaged.
- Burden on rest of the framework
Overload not only creates an impact where it is happening. But it also causes stress on the rest of the system. When motor get overloaded, In line gear system or conveyor belt system get under the stress. Which may leads to damage in gear system or in conveyor belt system. Overload is also dangerous for the near by appliances & for human beings itself.
- Complete damage to the setup
In overload, The level of damage is proportional to the level of overload. If overload is much higher & happening from a long time than there is complete possibility of complete damage. As discussed, Overload results in High inrush current which results wires get burnt after getting overheated.
pRECAUTIONARY MEASURES FOR OVERLOAD !
- Monitoring
Monitoring is the first step towards the prevention from overload. Factors like temperature, vibration, noise should be monitored on regular basis.
Moreover, Some of the electrical factors should also be recorded like voltage, Current, power & Energy consumption etc.
Due to continuous monitoring, Whenever, A little deviation happens, it get observed.
- Thermal overload Protection
As discussed above, In overload condition, It is the level of current which increases gradually. Electrical loads should be protected through back-up fuses or thermal overloads.
Whenever current crosses the level of thermal rating, it gets trip & supply get break.
- Servicing at regular intervals
In running system, chances of deterioration is always there. Safety from overload is not one time step rather it continuous step which should be involved in regular activities.
Cleaning, Lubrication & tightening should be done at regular intervals. Regular servicing makes the chances of overload minimal.
SUMMARY
- Overload refers to exceeding the capacity of electrical systems, leading to higher current consumption than rated limits.
- Overload can damage equipment like motors, which are designed to operate at specific voltages and currents.
- Damaged bearings and lack of lubrication contribute to overload conditions. Extra loading and obstructions also play a role. These factors lead to long-term degradation and reduced lifespan of systems.
- Monitoring electrical factors and implementing protective measures like thermal overload protection and regular servicing are crucial to prevent overload.
- If not addressed, overload can result in severe system damage and hazards to nearby equipment and individuals.
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