JPH08126192A - Open phase detector - Google Patents

Abstract

PURPOSE: To prevent burning of a motor, etc., by making the detection of an open phase available even for a phase which is not provided with a current sensor. CONSTITUTION: This equipment is provided with a first current sensor 3 which has a first iron core 3c wherein power lines of a first phase R and a third phase T are wound the different number of turns, a second current sensor 4 which has a second iron core 4c wherein a power line of a second phase S is wound the same number of turns as that of the first phase R, and an open- phase detector 10 which determines whether the first phase R and the second phase S are open-phase or not by receiving current values from the first and the second current sensor 3, 4 and finding the ratio of the two and then comparing the value with a preliminarily set threshold value. By this method, an open phase can be detected even for the third phase T which has no current transformer installed for it. As a result, the motor burnout due to the open-phase with respect to all the phases can be prevented without a remarkable increase in cost.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase loss detecting device applied to a refrigerating device or the like.

[0002]

2. Description of the Related Art FIG. 2 shows a conventional open phase detector for a refrigeration system. In FIG. 2, 01 is a load such as a compressor motor and a blower motor driven by a three-phase power source.

Reference numerals 03 and 04 denote current sensors for detecting current values flowing in the R phase and S phase, respectively, and the detected values are inputted to the calculating means 06 in the open phase detector 05. The calculation means 06 calculates the difference between the received R-phase current detection value and the received S-phase current value and outputs the calculation result to the comparison means 07.

A predetermined current difference (for example, 5 A) is stored in advance in the comparison means 07. This predetermined current difference is compared with the current difference between the R phase and the S phase received from the calculation means 06, and this current difference is When the difference is equal to or more than a predetermined current difference (for example, 5 A), it is determined that the phase is open, and the load 1 is stopped via the output means 08. That is, when | R-phase current value−S-phase current value | ≧ predetermined current difference, it is determined that the phase is open and the load is stopped.

FIG. 3 shows a change in current when one of the three-phase power supplies is open. While the load 01 is in normal operation, the R, S, and T phases have almost current values L, but when a power plug contact failure or disconnection occurs, for example, when the S phase is open, the S phase current is lost. The value decreases to a constant level N with a constant time lag, and the R-phase and T-phase current values increase to a constant level M with a constant time lag.

Therefore, in the conventional apparatus, the phase loss can be detected by setting the above-mentioned predetermined current difference to be less than | M-N |.

[0007]

In the conventional open-phase detecting device, when the T-phase to which the current sensor is not attached is open-phase, as is apparent from FIG. 3, the R-phase current value and the S-phase current are shown. Both values rise to a certain level as well,
Since there is no current difference between the two, the open phase could not be detected, and there was a risk that the operation would continue in the open phase and the load would burn out.

If a current sensor is attached to all three phases of R, S, and T, it is possible to compare all the current values of each phase and judge whether or not there is a phase loss. There is a problem that the cost for one sensor is extra. The present invention is intended to solve the above problems.

[0009]

In the open-phase detection device of the present invention, the first-phase power supply line is wound with a fixed number of turns, and the third-phase power supply line is wound with a different number of turns. A first current sensor formed by providing a second current sensor formed by providing a second iron core having a second-phase power supply wire wound in the same number of turns as the first phase, and The current value detected by each of the first and second current sensors is input, the ratio is calculated, and this is compared with a preset threshold value to determine whether the first phase and the third phase are open phases. It is characterized by having an open-phase detector for

[0010]

In the above, when the second phase is missing, the current value detected by the second current sensor becomes 0, so that the second phase is detected.

When the third phase is out of phase, the currents flowing through the first and second phases are √3 times the normal operation, respectively, but the ratio is the same as in the normal operation and is a constant ratio. Therefore, the upper and lower thresholds are set with the fixed range sandwiching this value as the open phase range.

Therefore, when the ratio of the current value detected by the first current sensor to the current value detected by the second current sensor falls within the range of this threshold value, it is determined that the third phase is out of phase. The determination can be made, and the open phase of the third phase is detected.

When the first phase is missing,
The currents flowing through the second and third phases are √ during normal operation.
Although the ratio becomes three times, the ratio is the ratio of the number of turns of the second-phase and third-phase power supply lines. Therefore, the upper or lower threshold value is set based on this ratio.

Therefore, when the ratio of the current value detected by the first current sensor to the current value detected by the second current sensor exceeds this threshold value, it is determined that the first phase is out of phase. Then, the open phase of the first phase is detected. In addition,
The threshold value used for detecting the open phase of the first phase is an upper limit value when the number of the third phases is larger than the number of turns of the first and second phases, and is a lower limit value when the number of turns is less.

From the above, a dedicated current transformer (hereinafter, C
It is possible to detect the open phase even for the third phase for which T) is not provided, and it is possible to prevent the burnout due to the open phase of the motor for all the phases without increasing the cost significantly. Become.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a phase loss detecting device according to an embodiment of the present invention.
This will be described below. The present embodiment shown in FIG. 1 is applied to open phase detection of a three-phase power supply having R, S, and T phases, which is connected to the motor 1 via a circuit breaker 11.

In the open-phase detector of this embodiment shown in FIG. 1, CT3b in which the R phase is wound twice and the T phase is wound once in the iron core 3c, and the current detector 3a connected to the CT3b.
The current sensor 3 and the iron core 4c formed by
It is provided with a current sensor 4 formed by a wound CT4b and a current detector 4a connected to the CT4b, and an open phase detector 10 to which the current sensors 3 and 4 are connected.

The open phase detector 10 is composed of current sensors 3 and 4.
To calculate the ratio of the current value detected by the current sensor 3 to the current value detected by the current sensor 4, and input the ratio of the current values respectively from the calculation means 5 to input the T phase. R for determining whether the phase is missing or not
The determining means 7 for determining whether or not the phase is the open phase, the determining means 8 for determining whether or not the S phase is the open phase by inputting the current value from the current sensor 3, and the determining means 6, 7, 8 respectively. It is formed by output means for inputting the determination result and shutting off the circuit breaker 4.

In the above, when the current detected by the current sensor 4 is 1 when the motor 1 is in a normal operating state,
The detection values of the current sensors 3 and 4 in each operating state are the values shown in Table 1.

[0020]

[Table 1]

For example, 0.9 and 1.1 are previously stored as threshold values in the judging means 6, and when the ratio of the current values is within this range, the threshold value is inputted from the calculating means 5 and the above-mentioned values are inputted. The judging means 6 judges that the phase is the T phase open phase and outputs the judgment result.

Further, for example, 0.7 is stored in advance as the threshold value in the judging means 7, and when the ratio of the current values is less than this value, the judging means 7 inputs this from the calculating means 5. Determines that the phase is an R-phase open phase and outputs the determination result. Further, when the judging means 8 inputs the current value 0 from the current sensor 4, it judges that the phase is the S phase open phase and outputs the judgment result.

The judgment results of the respective judging means 6, 7 and 8 are inputted to the output means 9, and when any one of the R, S and T phases is open, the output means 9 opens the circuit breaker 11. As a result, the power supply to the motor 1 is cut off to prevent the open phase operation and prevent the motor from burning.

Although the present embodiment describes the case of a balanced load in which the currents flowing through the respective phases are approximately equal, the threshold value can be used even in the case of an imbalanced load in which a three-phase load and a single-phase load are mixed. It can be applied by setting the value to an appropriate value. Further, the number of turns of the T phase with respect to the R and S phases of the current sensor is set to 2: 1.
However, it is possible to change this.

[0025]

The open phase detecting device of the present invention has a first phase and a third phase.
A first current sensor provided with a first iron core in which the phase power supply wire is wound with a different number of turns, and a second iron core in which the second phase power supply wire is wound with the same number of turns as the first phase are provided. The current value is input from the provided second current sensor and the first and second current sensors, the ratio is calculated, and this is compared with a preset threshold value, and the first phase and the third phase are open phase. By providing the open-phase detector that determines whether or not it is possible to detect the open-phase for the third phase that does not have a dedicated current transformer, all phases can be detected without a significant cost increase. It is possible to prevent burnout due to a missing phase of the motor.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a phase loss detection device according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a conventional open phase detection device.

FIG. 3 is an explanatory diagram in the case where one phase of a three-phase power source is missing.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 motor 3 current sensor 3a current detector 3b CT 3c iron core 4 current sensor 4a current detector 4b CT 4c iron core 5 computing means 6,7,8 judging means 9 output means 10 open phase detector

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshio Yamashita 3-1, Asahimachi, Nishibiwajima-cho, Nishikasugai-gun, Aichi Prefecture Mitsubishi Heavy Industries Air Conditioning Factory

Claims (1)

[Claims] 1. A first current sensor formed by providing a first iron core in which a first-phase power supply wire is wound with a fixed number of turns and a third-phase power supply wire is wound with a different number of turns. A second current sensor formed by providing a second iron core in which the second-phase power supply line is wound with the same number of turns as the first phase, and detected by the first and second current sensors, respectively. It is characterized in that it is provided with a phase loss detector for inputting the input current value, calculating a ratio thereof, and comparing the ratio with a preset threshold value to determine whether the first phase and the third phase are open phases. Phase loss detection device.