Phase sequence indicator

[crutschow]

I was thinking of a temperature sensor to warn in the case of a sensor overheat. Ideally in that situation it would power the system down to save the sensors.
..............

That makes perfect 20-20 hindsight sense, but the only thing that could cause overheating of the detectors was applying the incorrect phase-sequence to the cooler and that, of course, was not anticipated. I don't think anyone was even aware that the cooler would heat when run in the reverse direction.
As the joke goes, somebody did not to a list of "all unforeseen failures." unfortunately.

 

[spec]

That makes perfect 20-20 hindsight sense, but the only thing that could cause overheating of the detectors was applying the incorrect phase-sequence to the cooler and that, of course, was not anticipated. I don't think anyone was even aware that the cooler would heat when run in the reverse direction.
As the joke goes, somebody did not to a list of "all unforeseen failures." unfortunately.

That reasoning does not sound like you crutschow.

spec

 

[crutschow]

That reasoning does not sound like you crutschow.

I don't understand that comment.

 

[RODALCO]

The lack of a phase sequence detector cost my company dearly many years ago. I was working on one of the early FLIR (infrared) systems for the Army and it used a 3-phase, 400Hz powered helium cryogenic cooler for the focal-plane detectors. We had in working fine in one lab using 3-phase power from the wall-plug outlet supplied by the 400Hz rotary inverter in the building.
We then moved it to a larger lab in a different building and plugged it into the inverter outlet in that building. We turned in on and it seemed to be operating normally. Someone noticed that it sounded a little different but didn't think too much of it. They kept waiting for it to cool down, which usually took about 15-20 minutes at which point the IR picture starts to appear, but the display stayed dark. They started checking the unit and then realized that the cooling fans (also 3-phase) were rotating in the wrong direction, indicating incorrect phase. They immediately shut off the power, but it was too late. It no longer worked, even after they rewired the connector to correct the phase. They took the focal plane apart and found that the cooler rotating in the wrong direction acted to heat the detectors instead of cooling them, and they had gotten hot enough to ruin their detection ability.
Don't know what that cost to fix but it weren't cheap, as all 350 detectors were individually mounted and hand wired (it had a mechanical horizontal scan to generate the picture from a vertical array of detectors).
Of course after that, they closed the barn door, and installed a 3-phase sequence detector to remove the power to the cooler if the phase wasn't correct.

I use a simple electro-mechanical Phase Sequence indicator. (rotation meter)
It is basically a small three phase motor with alligator clips and potential lights.
No reliance upon batteries, as it draws the power from the mains.
As I work in the power industry we often have to connect large generators 300 to 1500 kVA during power shutdowns and it essential that phase sequence is checked prior to shutdown on the existing site transformer, before the generator is connected up ( which is clockwise ).
A lot of TX's on the power network have anti-clockwise rotation and the damage to three phase equipment can be massive if these checks are not carried out properly.
Also very important to mark the phase sequence on the panel door and refer it to the colour coding or marking of the terminals.
E.G. (Red, Yellow, Blue) - clock wise
or (A-B-C ), (R-S-T) (L1-L2-L3) clockwise or anti clockwise

 

[tomizett]

You can build one very simply from triacs/SCRs that requires no low-voltage power supply...

I'm damned if I can remember the circuit though!

 

[sachin88]

hello crutschow,
In the simulated circuit the ground points shown are supposed to be neutral of the 3 phase supply right?

 

[RODALCO]

This Kyoritsu 8031 is a very reliable meter.
I use a newer version now with fused leads.

The other is an older German meter I sometimes use as well.

 

[sachin88]

Hi RODALCO,
Actually i am developing a remote monitoring device for a three phase alternator. I want to keep the phase sequence indicator permanently fixed to my monitoring device. So i want to rig up the circuit of phase sequence indicator. This sequence indicator will be useful while connecting the alternator to the power grid.

 

[RODALCO]

The phase sequence shouldn't change when all equipment is connected up and working properly.
More concern might be a phase failure which can cause 3 phase motors to burn out.
Best is to detect a phase failure with a phase failure relay, or one relay on each phase with the contacts in series which can drop out the supply when one of the phases is lost.

 

[sachin88]

hello crutschow,
In the circuit across R3, R4, R7 voltage should be 5V DC right?

 

[MrAl]

Hi,

I remember phase sequencers that were much simpler than what i see here. I dont remember the circuits now though.
I remember the old ones had neon bulbs, and used passive circuit elements.
Maybe we can come up with a simple one.

 

[sachin88]

MrAl i agree with you.
even the circuit discussed here could work. But when i rigged up the circuit and connected 3 phase the zener diode of first (R) phase got burnt. Thats y i wanted to clarify about the circuit once again.

 

[sachin88]

Actual scenario is i have to synchronize 2 alternators. When load goes beyond the capacity of primary alternator second alternator should be connected in parallel to share the load. Voltage and frequency i am calculating using Arduino. Now checking the phase sequence is problem. I do not want to use external meter to check sequence. If the above circuit works then my job will be easier.

 

[RODALCO]

You need a synchronizer to parallel two generators.

 

[crutschow]

hello crutschow,
In the simulated circuit the ground points shown are supposed to be neutral of the 3 phase supply right?

Correct

But if you are going to synchronize two generators you need more than a phase sequence detector.
You need a synchronizer as Rodalco said.

 

[MrAl]

Hello again,

Oh wow, yeah that's an entirely different thing to have to do.
Just because two generators have the same phase rotation doesnt mean that they have the same phase.
It would be a disaster to connect them together even if you got A,B,C phases correct on each individual generator.

 

[crutschow]

A phase synchronizer can be quite simple.
For example an LED in a bridge with a simple current-limit circuit can be connected between the same phase of the two generators.
The LED will flicker if they have a slightly different frequency, but as the slave generator is adjusted to the proper frequency and phase, the LED will burn steady, and then go out when the two phases are close together in relative phase (within the threshold voltage of the circuit).
At that point it's generally safe to close the switch between the two generators.

You can use two such circuits for two of the phases, which will then also indicate if the phase sequences match.

If you told us you needed to synchronize two generators together in the beginning we could have saved a lot of wheel spinning here.

 

[sachin88]

I thought if i have a sequence indicator then while connecting the slave generator with the master , dark lamp could be used for parallel operation.

Could you please help me with the circuit as you explained above for three phase generator.

 

[RODALCO]

We used two lamps equally bright and one dark when I was in the military in the field in the early 80's..
Now we use electronic phase synchronizers who sense phase rotation and will not close the circuit breaker if rotation or phasing is wrong.

If a parallel is not correctly done, serious damage will occur a crankshaft can break in half or equipment ripped of the mountings.

 

[crutschow]

Here's an article on the three lamp technique including the one dark lamp, two equal brightness lamp connection.
That connection probably has more sensitivity to small phase differences than the all-lights-being-dark configuration (all lamps in phase).
Either connection will show incorrect phase sequence as well as phase match between the two generators.
Incandescent lamps work well for that but you would need two 220v lamps in series for each phase, since the maximum voltage across the lamps can be 440V when the two generators are 180 degrees out.