Essentially, in this case, the launches of the A.T.K.v.d. they do not create voltage sink effects in existing co-operating electric circuits / installations.
We will try to present the "direct" start of A.T.K.v.d. with hardwired logic automation circuit operation.
Power and automation circuit - Brief / descriptive explanation of operation
I set ON position:
fuse disconnector F1 of the power circuit of the A.T.K.b.d. and
the microauto F3 of its automation circuit.
We notice that the H2 operation standby indicator lights up through the closed auxiliary contact K1/31-32 of the K1 relay.
I press the start button S2, the relay coil K1/A1-A2 is activated, so:
the 3 main contacts of the relay K1, the self-retaining contact K1/13-14, the second open auxiliary contact K1/23-24 are activated at the same time, so the operation indicator light H1 lights up, while the operation standby indicator light H2 goes off through the closed auxiliary contact K1/31-32 of relay K1 which opens.
I press the stop button S1 and the coil of the relay K1 is deactivated, so the operation of the A.T.K.v.d. stops. which switches to its standby mode.
If during the normal operation of the A.T.K.b.d. happen e.g. an overload in the windings of the A.T.K.b.d., the bimetallic thermal F2 is activated, so:
the closed contact of the thermal F2/95-96 opens and the current to the coil of the relay K1/A1-A2 is interrupted, consequently stopping the operation of the A.T.K.b.d. which switches to its operating standby mode, while at the same time
the open contact of thermal F2/97-98 closes and its alarm H3 (siren) is activated.
After repairing the damage, the A.T.K.v.d. switches to its standby mode.
For the complete tranquility of the A.T.K.v.d. must be set to the OFF position:
fuse disconnector F1 of its power circuit and
micro-automatic F3 of its automation circuit.
Circuit with additional safety button So (mushroom type) and auxiliary circuit at low voltage 24V
Winding connection of three-phase motors
Three-phase asynchronous motors are connected either in star or delta depending on their supply voltage.
When the connection must be made to the PPC network, the motor supply voltage is 400V (polar voltage).
It is very important to choose the right connection because otherwise we will damage the engine.
To connect a delta motor to the PPC network, its nameplate must read:
400/690 or 400/690 D/Y or 400 V D
On old motors we will see that they say 380/660 V/Y or 380 V D
To connect a motor to the PPC network in a star, the plate must read:
230/400 or 230/400 V/Y or 400 VY
On old motors we will see that they say 220/380 D/Y or 380 VY
The reason is because the motor can be connected to a network, such as PPC, in one way (e.g. triangle), while in another network created by a generator or one Inverter can be connected to another
Let's take another example where the motor reads 400/690 D/Y
The first voltage 400 that is written corresponds to the connection D That is, if we have polar voltage (between two phases) as in the PPC network we must connect the delta motor.
The second voltage 690 listed corresponds to the Y connection. That is, if we have a polar voltage (between two phases) of 690V, as in the case of a generator, we must connect the motor in Star.
We have a winding connection: 415 D
That is, at 50 Hz we have a winding connection: 220-240/380-420 V/Y and at 60 Hz we have a winding connection: 250-280/440-480 V/Y
Internal connection of trif coils. Motor
Inside three-phase motors are three compound coils with ends (U1-U2, V1-V2, W1-W2) or (UX, VY, WZ).
We call them complex because they consist of other smaller ones which are connected to each other in series, parallel or complex depending on the type of machine.
The six ends of the windings go to six terminals on the motor junction box and in the way shown in the picture below.
each of the ends of the three windings are connected together forming a common node.
In the delta connection the two ends of each winding are connected to each end of the other two windings.
The above two connections are achieved with special strips that we place on the windings in the terminal box. For the triangle three blades are needed, while for the star two.
Comparison of the two star and delta connections
Suppose that I connect two identical motors to the same network (next figure). Left in a star and right in a triangle.
1) In the star connection we notice that while we apply 400V polar voltage to the motor, its coils are supplied with 230V. So the motor coils should be designed to operate at 230V.
In the delta connection we notice that while we apply a 400V polar voltage to the motor, its coils are also supplied with 400V. So the motor coils should be designed to operate at 400V.
2) In the star connection the current flowing through each winding of the motor If is equal to the current of the network IY, that is If=IY.
In the delta connection the current flowing through each winding of the motor If is smaller by 1.73 times than the current of the mains Id, that is If=Id/1.73
In star connection the motor current is three times less than in delta connection as shown below:
, in star connection the motor will work normally but in delta connection they will be destroyed immediately due to higher voltage.
Which motors can be connected with a Y/D star-delta switch
To connect a three-phase motor to the network, the pole voltage of the network must coincide with one of the operating voltages of the motor, which are indicated on its nameplate. The mains connection possibilities are given in the table below (the voltage that cannot be used is written in fine print).
In general, to connect a star motor to the PPC network, the nameplate should read 230/400 DY or 400 Y.
To connect a delta motor to the PPC network, the nameplate should read 400/690 DY or 400 D
From the above voltages, the only motor that can be connected with a star-delta switch is the one indicated on the 400D nameplate
To connect a motor to the PPC network in a star, the plate must read:
230/400 or 230/400 V/Y or 400 VY
On old motors we will see that they say 220/380 D/Y or 380 VY
The reason is because the motor can be connected to a network, such as PPC, in one way (e.g. triangle), while in another network created by a generator or one Inverter can be connected to another
Let's take another example where the motor reads 400/690 D/Y
The first voltage 400 that is written corresponds to the connection D That is, if we have polar voltage (between two phases) as in the PPC network we must connect the delta motor.
The second voltage 690 listed corresponds to the Y connection. That is, if we have a polar voltage (between two phases) of 690V, as in the case of a generator, we must connect the motor in Star.
We have a winding connection: 415 D
Internal connection of trif coils. Motor
Inside three-phase motors are three compound coils with ends (U1-U2, V1-V2, W1-W2) or (UX, VY, WZ).
We call them complex because they consist of other smaller ones which are connected to each other in series, parallel or complex depending on the type of machine.
Suppose that I connect two identical motors to the same network (next figure). Left in a star and right in a triangle.
In the delta connection we notice that while we apply a 400V polar voltage to the motor, its coils are also supplied with 400V. So the motor coils should be designed to operate at 400V.
2) In the star connection the current flowing through each winding of the motor If is equal to the current of the network IY, that is If=IY.
In the delta connection the current flowing through each winding of the motor If is smaller by 1.73 times than the current of the mains Id, that is If=Id/1.73
In star connection the motor current is three times less than in delta connection as shown below:
, in star connection the motor will work normally but in delta connection they will be destroyed immediately due to higher voltage.
Which motors can be connected with a Y/D star-delta switch
To connect a three-phase motor to the network, the pole voltage of the network must coincide with one of the operating voltages of the motor, which are indicated on its nameplate. The mains connection possibilities are given in the table below (the voltage that cannot be used is written in fine print).
In general, to connect a star motor to the PPC network, the nameplate should read 230/400 DY or 400 Y.
To connect a delta motor to the PPC network, the nameplate should read 400/690 DY or 400 D
From the above voltages, the only motor that can be connected with a star-delta switch is the one indicated on the 400D nameplate
To thank the ELECTRICAL SCIENTISTS of the 1st EPAS OAED THESSALONIKI for the amazing technological content and the wonderful articles they publish on their blog.
