Motor Acceleration Study and Analysis Services in UAE

Motor Starting Study and Analysis recognises the probable voltage dip and acceleration time for a motor and the consequences of motor starting on a system. It assesses proper starting and running of motors on load with given system inertia without causing tripping or instability in the system. Other starting methods, such as autotransformer start, reactor, across-the-line, capacitor, or are also studied. If system voltage dips are a concern, Carelabs will propose the appropriate solutions.

The starting current of most AC motors is several times the normal full rated load current when starting from full line voltage. These large current requirements can result in nuisance tripping of protection breakers, excessive running currents, drop in terminal voltage etc. Dimming of lights as motors start up is a clear indicator that the power system may need investigation. It may have insufficient capacity or a better motor starting strategy may be required.

Why is Motor Starting Study and Analysis Done?

The starting torque varies directly as the square of the applied voltage. Thus excessive starting current results in drop in terminal voltage and may result in the following:

• Failure of motor starting due to low starting torques.
• Unnecessary operation of under voltage relays.
• Stalling of other running motors connected to the network.
• Voltage dips at the power sources and consequent flicker in the lighting system.

The most serious effect of a large voltage drop or brown out is an increase in current of all devices servicing a constant load. Static power supplies such as computers and ballasts for lighting must increase the current to deliver the same amount of power resulting in overheating and eventually burn-out. Other induction motors operating at sync speed will increase their current draw until it reaches maximum current and may slip out of sync further increasing the current demand.

Motor starting studies assists in the choice of the proper motor design, the best method of starting and the proper system design for reducing the effect of the motor starting. Motor starting studies are essential in determining the impact on system voltage during starting and in establishing whether the motor will start satisfactorily and come up to speed. The result of these studies allows engineers

• To start motors individually
• Use load transitioning to test the impact of fast bus transfer voltage
• Enable load-group actions.

In various electrical installations in industrial and commercial units, engineers are continuously verifying and stimulating motor starting and acceleration systems to determine whether they are working properly. The essential areas they must evaluate are the starting, stopping and restarting of electrical motors.

What is Done During Motor Starting Study and Analysis?

Motor starting studies vary from instantaneous start-up of one or more of the largest motors to detailed simulation of the current, voltage and speed with respect to time. This allows engineers to test different slow start mechanisms ranging from auto-transformers to variable frequency drives and determine the optimum settings for start-up time and effect on the system. If a starting device is needed, its characteristics and ratings can be easily determined.

Study of motor starting methods can be done using both static and dynamic simulation methods. These techniques have their own advantages and disadvantages. We believe mainly in transient or dynamic motor starting studies that reproduce measured motor starting conditions.

• Load flow type solution with the observed starting impedance of the motor modelled as part of network modelling.
• Short circuit method type of calculations considering pre-fault short circuit conditions and using voltage drop calculations considering motor starting currents. Alternatively
• Where precise dynamic model of the motor electric circuit and load – torque characteristics are existing, dynamic model of the motor can be utilised in traditional transient stability algorithm to evaluate the impact of the motor starting.
• When there is a lack of precise model information, transient stability studies can be utilised, where the measured starting current can be applied as a nodal injection at the motor bus as a dynamic event and the system response to this dynamic event can be measured.

How is Motor Starting Study and Analysis Performed?

The output torque is related to square of the voltage. If an AC induction or synchronous motor is started while attached to a mechanical load on the shaft, inrush current can be up to 6 times full-load current and will be drawn for a longer time. The power system while offering normal service to the remainder of the industrial or commercial system, must also be capable to source enough inrush current to any motor

As electrical consultants, motor starting studies help to improve the reliability engineering for the entire building system and industrial.