how these relays will get the reference as regards R S T phases? i think since in both direction pf phasors will cause the same wave shapes and there must be a reference , do we refer any true rst phases at first or it will somehow automatically dedect the RST phases? ( I guess it is impossible since both direnction of phasors will get the same wave shapes )
phase sequence relays
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beanland
Senior Member
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- Vancouver, WA
Rotation
Rotation
Are you asking about rotation? In this case, the reference phase is arbitrary. It is voltage, not current that is used as the reference. Really, it does matter if the rotation is ABC, BCA, or CAB. It is all the same.
Rotation
Are you asking about rotation? In this case, the reference phase is arbitrary. It is voltage, not current that is used as the reference. Really, it does matter if the rotation is ABC, BCA, or CAB. It is all the same.
zog
Senior Member
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- Charlotte, NC
There are many different types of shase sequesnce relays that use different menthods of sensing, I suggest you Google "Phase sequence relays" to get a better idea of what you are asking.
beanland
Senior Member
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- Vancouver, WA
Rotameter
Rotameter
The early rotation indicators are nothing more than a small 3-phase motor. When hooked up the the three conductors, they rotate slowly so that the human observer can see the rotation. Nothing much to them.
The other technique uses lights and a capacitor to indicate the direction of rotation.
Rotameter
The early rotation indicators are nothing more than a small 3-phase motor. When hooked up the the three conductors, they rotate slowly so that the human observer can see the rotation. Nothing much to them.
The other technique uses lights and a capacitor to indicate the direction of rotation.
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- San Francisco Bay Area, CA, USA
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- Electrical Engineer
Although as mentioned there are several ways it is done, the simplest is to just look at the 3 states of peak voltages and a time clock. To make it easier, name them;
R-S = 1
S-T = 2
T-R = 3
If 1-peak is followed by 2-peak, then rotation is RST
If 1-peak is followed by 3-peak, then rotation is TSR
R-S = 1
S-T = 2
T-R = 3
If 1-peak is followed by 2-peak, then rotation is RST
If 1-peak is followed by 3-peak, then rotation is TSR
excuse me but i couldnt get what i want, now let me ask this way:
these relays will only trip the moment when the two phase interchange or we just keep a RST or RTS sequence in its memory at first and then trip only in the reversal of this sequence? i mean if we can define a true direction for us and want to make it trip if it reverses? i hope i can express it well. first case is related to just a" change" heedless of the first sequence and the second one is related to a predefined sequence (two posible sequence ) so that the same relay can be used with two motors separately one is turning clockwise the other turning anti-clockwise at different times...
these relays will only trip the moment when the two phase interchange or we just keep a RST or RTS sequence in its memory at first and then trip only in the reversal of this sequence? i mean if we can define a true direction for us and want to make it trip if it reverses? i hope i can express it well. first case is related to just a" change" heedless of the first sequence and the second one is related to a predefined sequence (two posible sequence ) so that the same relay can be used with two motors separately one is turning clockwise the other turning anti-clockwise at different times...
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- San Francisco Bay Area, CA, USA
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- Electrical Engineer
The answer is, some do, some don't. In general, the cheaper ones do not test and compare, they just compare to a preset sequence and you must make your system match it. More sophisticated ($$) versions check the first time they are energized and compare from there on, or give you the option in programming.
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- San Francisco Bay Area, CA, USA
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- Electrical Engineer
Change the last sentence;
More sophisticated ($$) versions check when told to (i.e. the first time they are energized) and compare from there on, or give you the option in programming.
More sophisticated ($$) versions check when told to (i.e. the first time they are energized) and compare from there on, or give you the option in programming.
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as far as ı Know there is only one RST phase throughout a country grid right? so if u use a "RST " preset sequence relay and if u need afterwards to make a motor run reverse so u cant use this relay any more true?
So a developed relay should be able de discern a RST and RTS sequence? so these two sequence will create a real physical magnetic rotating field and i guess it can be only two different direction a clock-wise and an anti-clockwise true?
but i think when u look at the three phase represantation of a sinewaves i cant see a difference between RST and RTS so i cant see how they create two different magnetic field direction? just change the names of the phases
i am confused in this subject. Pls clarify a bit more...
So a developed relay should be able de discern a RST and RTS sequence? so these two sequence will create a real physical magnetic rotating field and i guess it can be only two different direction a clock-wise and an anti-clockwise true?
but i think when u look at the three phase represantation of a sinewaves i cant see a difference between RST and RTS so i cant see how they create two different magnetic field direction? just change the names of the phases
i am confused in this subject. Pls clarify a bit more...
in fact i think i can guess that the dedection is up to the effect of the currents not voltage indeed.But so it means all the developed relays should have electrodynamical components to dedect the direction of the phases seeing the result of the magnetic forces created by these sequences and it means a coarsa design isnt it? maybe there is another method for dedecting this? maybe=?
mivey
Senior Member
By looking at the sine waves, you can see the timing and identify the positive sequence and label them correctly. If someone had already labeled the waves before you got there, you might see RST or you might see RTS.but i think when u look at the three phase represantation of a sinewaves i cant see a difference between RST and RTS so i cant see how they create two different magnetic field direction? just change the names of the phases
i am confused in this subject. Pls clarify a bit more...
mivey
Senior Member
The currents are load dependent so you must look at the voltages. Suppose you had a resistor + capacitor combination on one phase and an inductor + resistor combination on a second phase and some combination of capacitors & inductors & resistances on the third? The current phasors could be all over the place.
yeaah u are right, it is not up to the currents really, so how can a relay dedect the sequence?? when i draw RST and RTS i think h both of them are same arent they? no matter what names they have, even if u reverse two of them it is again three phase with 120 degree apart ??? i am confused really..
mivey
Senior Member
You have to keep up with your labels. The order in which they reach the positive peak will be different.
Plot the following three curves:
A=SQRT(2)*120*COS(2*Pi*60*t+0*Pi/180)
B=SQRT(2)*120*COS(2*Pi*60*t-120*Pi/180)
C=SQRT(2)*120*COS(2*Pi*60*t-240*Pi/180)
Let t vary from 0 to 1/60 in increments of 1/1200 or so. Let A be red, B be yellow, and C be blue.
The graph will show 3 sinusoidals. As you move from left to right, the first peak will be the red wave at 0 seconds, the next peak will be the yellow wave at 0.0055556 seconds, and the next will be the blue at 0.0111111 seconds. That is an ABC sequence.
Now Plot the following three curves:
A=SQRT(2)*120*COS(2*Pi*60*t+0*Pi/180)
C=SQRT(2)*120*COS(2*Pi*60*t-120*Pi/180)
B=SQRT(2)*120*COS(2*Pi*60*t-240*Pi/180)
Let t vary from 0 to 1/60 in increments of 1/1200 or so. Again, let A be red, B be yellow, and C be blue.
The graph will again show 3 sinusoidals. As you move from left to right, the first peak will be the red wave at 0 seconds, the next peak will be the blue wave at 0.0055556 seconds, and the next will be the yellow at 0.0111111 seconds. That is an ACB sequence.
oh thank u it is nice but what i cant understand is these two have the same magnitudes at the same times, so how a relay can distinguish between these two sequences if it has not any preset reference? namely a relay will need to have a reference to be able to say that one of these is R and the first the other.......
so in fact here is a matter of reference, what is exactly RST phases? if there is 120 degrees between three phasors it means a potential RST or RTS but what is the reference exactl? for example a grid phase sequence in my country is RST so how can a relay have a preset or not preset phase to be able to decide the direction? i wonder how a technique is used here...
i am really appreciating what u wrote above indeed but i can not solve the direction and its dedection issue..
so in fact here is a matter of reference, what is exactly RST phases? if there is 120 degrees between three phasors it means a potential RST or RTS but what is the reference exactl? for example a grid phase sequence in my country is RST so how can a relay have a preset or not preset phase to be able to decide the direction? i wonder how a technique is used here...
i am really appreciating what u wrote above indeed but i can not solve the direction and its dedection issue..
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mivey
Senior Member
They do not have the same magnitude at the same time. They only have the same magnitude in the frequency domain, not the time domain.
Only one will be at the peak value at a time. The difference in this time is how you can get the sequence.
in fact the gist of my problem here is that one of our friends said above (perhaps u mivey) there are some relays which can find phases themselves and break the supply if it reverses so it is not problem that even if the supply is RTS and not RST (reverse of the conventional sequence) at the moment of connection and motor runs and after a while if the sequence returns back to its conventional sequence so the relay will break the supply since at the moment it defined the sequence of the supply it takes the sequence at that moment as reference so that it will break if it reverses,
generally i see relays which have defined supply phase names as RST and it means if the conventional supply is RST so u cant run a motor in reverse direction true?
but if the relay is programmable so u can preset the sequence as RTS and it will run reverse and there is no problem from then on true?
anyway i wont ask any question about this thank u for all ur help tries...
generally i see relays which have defined supply phase names as RST and it means if the conventional supply is RST so u cant run a motor in reverse direction true?
but if the relay is programmable so u can preset the sequence as RTS and it will run reverse and there is no problem from then on true?
anyway i wont ask any question about this thank u for all ur help tries...
as u said only names change, the next peaks will be at the same time with other scheme, in reality there is no need to draw a picture, if they have 120 degree in both cases it means they have the same values at the same times exept that only phase names changing,
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