Braking application for electric motor are used widely around the world for equipment or machinery such as electric crane,barrel machine,electrical train,lift or for industrial drive.
Basically the braking system for electric motor fundamental is a one mechanism to created retarding torque to stop the motor rotation with sudden or slow stop depend on application system.
Not all electric motor must have braking system.Normally it used for drive application that have lot of energy stored in rotating part for machine or equipment.It also used for driven system that required rapid deceleration and can controlled for accident or emergency situation.
For the method to created a braking torque and quick stop for induction motor,it have a two basic method such as :
1) Design the controller to made motor operated as a generator.Example is d.c injector method.
2) Created a device to reversing the rotation to created load until it stop.Example is plugging method.
2) Created a device to reversing the rotation to created load until it stop.Example is plugging method.
In a new technologies for equipment or machinery,braking system have a intelligent controller to created a high accuracy for stop the electric motor.
It also design with full safety device and application to ensure for comfortable and safety priority to human being.I will explain detail about braking method for d.c injection and plugging in my next post.
Cable termination is important when we install equipment,machine,induction motor,power supply distribution and many more.We use a cable lug to connect the electrical cable with terminal or busbar. The right method to install cable lug is important to ensure the termination is perfect and tight to avoid sparking.It can cause the damage of cable or the [...]
Why temporary electrical power supply important for construction area? When working at construction area or for temporary work space,the electrical supplies that we provided can save our times and can speed up the working progress.Because the power tools and lighting or others equipment needed the power supply to completed the tasks. We must ensure the [...]
When we planning to wiring the bathroom,we must consider the several electrical wiring regulation are specified.In this room almost in wet condition can cause the electric shock if we not proper design according the regulations. Basically bathroom containing a fixed bath tub,shower basin,sink ,etc.So with additional regulations,it can reduce the chance of electric shock due [...]
What is a cable lug? This device is very common used for connecting cable to the electrical installation such as power distributor,instrument,automation,motor control and etc.It is designed for easy install and remove for repairing or maintenance jobs.It also can avoid a cable broken or burn due to sparky if cable connection not tight. Now in [...]
WHAT IS CONDUCTOR OR CABLE SPLICES? It is the method to jointing and two of cable or conductor with a good quality and safe for electrical application.In electrical work, the connection cable is quite important and should be taken seriously, if it is the wrong way, this will lead to an accident or damage
Motor Overload Protection
Overload protection is installed in the main control circuit or power line ofmotor to protect from damage due to mechanical malfunction overloadconditions when it is running.
The effect of an overload is an excessive rise in temperature in the motor windings due to current higher than full load current.
Properly sized overload protectiondisconnects the motor from the powersupply when the heat generated in the motor circuit or windings approaches a damaging level for any reason. The larger the overload, the more quickly the temperature will increase to a point that is damaging to the insulation and lubrication of the motor.
The over current device will not react to this low level overload. The motor overload device prevents this type of problem from severely damaging the motor and also provide protection for the circuit conductors since it is rated for the same or less current as the conductors.
Basic Operating Principle
o
The eutectic alloy in the heater element is a material that goes from a solid to liquid state without going through an intermediate putty stage.
The eutectic alloy in the heater element is a material that goes from a solid to liquid state without going through an intermediate putty stage.
o
When the motor current exceeds the rated value, the temperature will rise to a point where the alloy melts; the ratchet wheel is then free to rotate, and the contact pawl moves upward under spring pressure allowing the control circuit contacts to open.
When the motor current exceeds the rated value, the temperature will rise to a point where the alloy melts; the ratchet wheel is then free to rotate, and the contact pawl moves upward under spring pressure allowing the control circuit contacts to open.
o
After the heater element cools, the ratchet wheel will again be held stationary and the overload contacts can be reset.
After the heater element cools, the ratchet wheel will again be held stationary and the overload contacts can be reset.
Designation of overload protection
Overload devices are designed to allow high currents to flow briefly in the motor to allow for:
o
Short duration overloads such as a slug of product going through a system.
Short duration overloads such as a slug of product going through a system.
If the motor inlets and outlets are covered by a blanket of lint or if a bearing should begin to lock, excessive heating of the motor windings will “overload” the motors insulation which could damage the motor.
A
motor
overloadrelayis an electro-mechanical relay that is operated by heat developed in the relay.
When the level of
current
in acircuitreaches a preset value, the increasedtemperatureopens a set of contacts.
The increased temperature opens the contacts through a bimetallic strip or by melting an alloy that activates a mechanism that opens the contacts.This time i explain detail about common types of
overload
relay for motorcontrol.
1) Thermal overload relays
o
Melting alloy
Melting alloy
These are probably the most popular type of overload
protection.The motor
currentpasses through a small heater winding and under overload conditions.
The heat causes a special solder to melt allowing a ratchet wheel to spin thus opening thecontrol
circuit
contacts.It must be reset by hand operation and Heater coil and solder pot in one unit non-tamperable.
o
Bi-metallic strip
Bi-metallic strip
This design uses a bimetal strip associated with a
current-carrying heater coil.When an overload occurs, the heat causes the bimetal to deflect and actuate a tripping mechanism which opens a set of contacts in the control circuit interrupting
powerto the coil and opening the power contacts.
Most relays are adjustable over a range from 85% to 115% of their value.They are available with ambient compensation. An ambient compensated devices’ trip point is not affected by ambient temperature and performs consistently at the same value of
current
When the level of
current
in the circuit reaches a preset value, the increasedmagneticfield opens a set of contacts.
Electromagnetic overload relays operate on the magnetic action of the load
current
flowing through a coil.
When the load current becomes too high, a plunger is pulled up into the coil interrupting the circuit.The tripping current is adjusted by altering the initial position of the plunger with respect to the coil.
Overload
relay is the one of importantdevice
for motorcontrol.It canpreventour motor from overheat or winding burning due overload ofampere.
We need to setting the value of overload relay properly depend on our application and motor full load
ampere.If we setting low from
FLA,it can cause motor trip c0ntinues and process not running smoothly.
But if we setting to high from FLA,the overload relay cannot protect the motor if overload happen.It can cause the motor failure or winding burns.So we must calculated and get a right setting for the overload relay.
1) IB ≤ In ≤ IZ
IB = Anticipated operating current of the circuit
IZ = Current carrying capacity of conductor or cable or Motor
In = Rated current of protective device
2) I2 ≤ 1,45 x IZ
For adjustable protective devices, In corresponds to the value set.
I2 = The
current
which causes tripping of the protective device under the conditions specified in theequipmentregulations (high test current).
Common practice
Normally for overload relay setting depend on
FLA ( Full Load Ampere )
of motor.We can see at the NAMEPLATE of motor.Normally setting for overload is 5% until 10 % more than FLA.
But it is depend on operation and functional of motor.For more detail setting,please refer manual guide of motor from manufacture.
We also can setting overload relay value depend on value of service factor motor.Example if service factor 1.15,we can setting 125% from FLA and if service factor is 1.0,we can setting 115% from FLA of motor.
Manual and automatic reset.
Normally,overload relay have this 2 reset function selection.We can choose manual or automatic reset after it trigger overload from motor.
I recommended for manual reset function because we can know when it trip and we cantroubleshooting
the
root causefor tripping issue.So after we found the root cause,we can reset back the overload relay and can continue the operation.
A
motor
overloadrelayis an electro-mechanical relay that is operated by heat developed in the relay.
When the level of
current
in acircuitreaches a preset value, the increasedtemperatureopens a set of contacts.
The increased temperature opens the contacts through a bimetallic strip or by melting an alloy that activates a mechanism that opens the contacts.This time i explain detail about common types of
overload
relay for motorcontrol.
1) Thermal overload relays
o
Melting alloy
Melting alloy
These are probably the most popular type of overload
protection.The motor
currentpasses through a small heater winding and under overload conditions.
The heat causes a special solder to melt allowing a ratchet wheel to spin thus opening thecontrol
circuit
contacts.It must be reset by hand operation and Heater coil and solder pot in one unit non-tamperable.
o
Bi-metallic strip
Bi-metallic strip
This design uses a bimetal strip associated with a
current-carrying heater coil.When an overload occurs, the heat causes the bimetal to deflect and actuate a tripping mechanism which opens a set of contacts in the control circuit interrupting
powerto the coil and opening the power contacts.
Most relays are adjustable over a range from 85% to 115% of their value.They are available with ambient compensation. An ambient compensated devices’ trip point is not affected by ambient temperature and performs consistently at the same value of
current.
When the level of
current
in the circuit reaches a preset value, the increasedmagneticfield opens a set of contacts.
Electromagnetic overload relays operate on the magnetic action of the load
current
flowing through a coil.
When the load current becomes too high, a plunger is pulled up into the coil interrupting the circuit.The tripping current is adjusted by altering the initial position of the plunger with respect to the coil.
Basically automatic
voltage
regulatorforgeneratorhave a 2 mode selection.It is with full automaticfunctionand manual function.
I already discuss about
AVR
function and basic operation in my last post.Please refer tobasic of automatic voltage regulator.i hope it can make a clear view and understanding aboutAVRfunction ingenerator.
This time i want share some
informationabout
controllermethodthat commonly used forAVRfor generator.For latest design of AVR,manufacture put a two(2) selection for AVRcontrollermode.It is Automatic and Manual mode.
This selection of AVR controller mode depend on our system and
current
application for generator.I explain detail about this two AVR controller mode.
For automatic mode controller is a normal selection when running in standard generator for generated
power
supply.This mode controlled by automatic system that designed and setting by manufacture to get standard output.
Generators are normally required to deliver from zero to rated output over a voltage range of ±5%, at
power
factors from 0.8–0.9 lag to 0.9 lead.
The a.v.r. setting controls must provide the appropriate range of excitation as well as a voltage down to about 85% of nominal at no-load.Accuracy of
control
is normally between ±2.5% and ±1% of set value over the load range.
Manual control mode.
For manual control mode,it usually used for back-up system from automatic mode if it malfunction or needed to manual setting for generator output.
In others situation,many bigger machine needed a huge power
supply
and it not sufficient excerpt generator running in automatic mode and the manual control setting only used for the initial commissioning during setup.
Most voltage regulators, when operating in automatic, are provided with ‘manual follow-up’ which ensures that the manual setting matches the automatic setting so that if failure of the automatic system causes a ‘trip to manual’ this will not result in any change of set-point.
A balance meter may be provided so that if changeover is to be made manually, a check can be made before effecting the change.Please refer to manufacture if you not sure how to used manual mode to avoid serious damage to the generator.
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