JPS6211159Y2 - - Google Patents

Description

[Detailed description of the invention] This invention detects open-phase accidents in three-phase motors, etc.
The present invention relates to an open phase detection circuit that protects a motor.

Conventional circuits of this type rectify the load current and
There are various methods such as the ripple method that detects the ripple change and the method that compares the positive and negative phase components, but these methods have problems such as being susceptible to waveform distortion and not being able to detect the negative phase and the missing phase separately. .

The present invention aims to improve the above-mentioned drawbacks, and will be explained below based on the drawings.

Figure 1 shows an embodiment of the present invention, and in the figure
R ₁ to _{R 13} are resistors, CT ₁ and CT ₂ are current transformers, TR ₁ to _{TR 4}
are transistors, IC ₁ to _{IC 3} are AND elements, IC ₄ is an OR element, IC ₅ is a comparison amplifier, D ₁ to D ₆ are diodes, C ₁ to C ₃ are capacitors, RA is a relay, and E is a DC power supply. .

The secondary terminals of the current transformers CT ₁ and CT ₂ that detect the load current are connected to resistors R ₁ and R ₂ , respectively, and further V-connected to convert the load current into three-phase voltage.

The first phase of said three-phase voltage is applied to the base of transistor TR ₁ via resistor R ₃ and likewise the second phase.
The third phase is applied to the base of the transistor TR ₂ via the resistor R ₄ and the third phase is applied to the base of the transistor TR ₃ via the resistor R ₅ .

The diodes D ₁ to _{D 3} are connected to the transistor TR ₁
~ This is a reverse voltage protection diode between the base and emitter of TR ₃ .

Since the collector of the transistor _TR1 is connected to the DC power supply E via the resistor _R6 , when the first phase of the three-phase voltage becomes positive, the transistor _TR1
It becomes ON state and the collector potential becomes low potential.
Conversely, when the first phase of the three-phase voltage becomes negative, the transistor _TR1 is turned off and the collector potential becomes high.

That is, the transistor _TR1 is connected to the first voltage of the three phase voltages.
ON/OFF depending on whether the phase voltage becomes positive or negative
This is repeated to generate a pulse synchronized with the first phase voltage.

Similarly, the transistor TR ₂ generates a pulse synchronized with the second phase voltage of the three-phase voltage, and the transistor TR ₃ generates a pulse synchronized with the third phase voltage of the three-phase voltage. . (Fig. 2 V ₁ ,
(See V ₂ , V ₃ ) The collector of the transistor TR ₁ is an AND element.
Similarly, the collector of the transistor TR ₂ is connected to the gates of AND elements IC _{1 and} IC ₂ , and the collector of the transistor TR ₃ is connected to the gates of AND elements _{IC 2 and} IC ₃ . has been done.
That is, the AND element IC ₁ outputs a high potential signal only when the first phase voltage and the second phase voltage of the three-phase voltages are both negative. Similarly, AND element IC ₂ outputs a high potential signal only when the second phase voltage and third phase voltage are both negative, and AND element IC ₃ outputs a high potential signal only when the third phase voltage and first phase voltage are both negative. outputs a high potential signal. The respective outputs of the AND elements IC ₁ to _{IC 3} are input to the gate of the OR element IC ₄ , and each overlap angle of each phase is output as a high potential signal (second
Figure _V4 ). Further, the output of the OR element IC ₄ is connected to an integrating circuit composed of a resistor R ₉ and a capacitor C ₁ , and the overlapping angle signals of each phase are converted into triangular wave signals (V ₅ in FIG. 2).

The midpoint of the first integrating circuit is connected to a differentiating circuit composed of a capacitor C ₂ , a diode D ₅ , and a resistor R ₁₀ to detect the ripple voltage of the triangular wave signal. Capacitor C ₃ connected in parallel with said resistor R ₁₀
is a smoothing capacitor, and the diode _D5 is a diode for preventing discharge of the capacitor _C3 . Further, the diode _D4 is a diode for discharging the capacitor _C2 .

The voltage of the resistor _R10 is input to the comparison amplifier _IC5 , and is compared with a voltage (hereinafter referred to as reference voltage) determined by a voltage dividing circuit constituted by resistors _R11 and _R12 . The output of the comparison amplifier IC ₅ is connected to the base of the transistor TR ₄ via a resistor R ₁₃ .
The collector of the transistor TR ₄ is connected to the relay RA
It is connected to the DC power supply E via. A diode _D6 connected in parallel to the relay RA is a surge protection diode for the transistor _TR4 .

When the load current is a balanced three-phase current, the overlapping angle of each phase is 60°, and the overlap angle of each phase is 60° as shown in V ₄ in Figure 2.
It becomes an ON/OFF signal. 60° each ON・
The OFF signal is converted into a triangular wave by the integration circuit,
Only the ripple voltage is detected by the differentiating circuit.
The detected ripple voltage is compared in the comparison amplifier IC ₅ , but since the reference voltage is set higher, the output remains at a low potential. That is, the transistor _TR4 is in an OFF state, and the relay RA is also in a non-energized state.

Next, for example, if the S phase is open, the first and third phases of the three-phase voltage will be in phase, and the overlapping angle of each phase will be 180 degrees. As shown in V ₄ in Figure 3, it becomes an ON/OFF signal in 180° increments, and is similarly converted into a triangular wave to detect ripple voltage, but the ripple voltage during an open phase is larger than the ripple voltage during balanced three-phase operation. It's summery. Therefore, since the reference voltage is set lower than the ripple voltage at the time of phase loss, the output of the comparison amplifier IC ₅ becomes a high potential and outputs a detection signal.

That is, the transistor _TR4 is turned on, the relay RA is also excited, and an open phase detection signal is output. It goes without saying that by appropriately setting the reference voltage, it is also possible to detect unbalance as shown in FIG.

As explained above, the present invention detects the overlapping angle of each phase current and converts the change in the overlapping angle into ripple voltage to detect open phase or unbalance, so the load current is not distorted. Needless to say, even if the waveform is different, it will not be affected.

Although this embodiment has been described using an AND element and an OR element, it goes without saying that similar effects can be obtained by using a NAND element or a NOR element.

Further, in the above embodiment, the case where two current transformers are used to detect the load current has been illustrated and described, but it goes without saying that the same effect can be obtained even if three current transformers are used.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing one embodiment of the present invention;
The figure shows an operation pattern during balanced operation, FIG. 3 shows an operation pattern during open phase, and FIG. 4 shows an operation pattern during unbalanced operation. In the figure, R ₁ to _{R 13} are resistors, CT ₁ and CT ₂ are current transformers, TR ₁ to TR ₄ are transistors, IC ₁ to _{IC 3} are AND elements, IC ₄ is an OR element, and IC ₅ is a comparison amplifier. , D ₁
~ _D6 is a diode, _C1 ~ _C3 are capacitors, RA is a relay, and E is a DC power supply.

Claims (1)

[Scope of utility model registration request] Determines whether each phase of the three-phase load current detected by the load current detector is positive or negative, and outputs a pulse signal corresponding to the positive or negative of each phase of the three-phase load current. an overlap angle detection circuit that receives each output of the pulse generation circuit as input and outputs one pulse signal according to the overlap angle of each phase, and integrates the output of this detection circuit to generate a triangular wave signal. Equipped with a CR integration circuit,
An open phase detection circuit characterized in that an open phase or unbalanced phase in a three-phase circuit is detected by detecting the ripple voltage of the CR integrating circuit.