DK178815B1 - Power Transducer without Power Circuit for Circuit Breakers - Google Patents

Abstract

The object of the invention is to simplify the construction of current transducers, which are widely used within low voltage coupling components. The invention removes the energy-generating circuit from the combined current transducer, and adds additional functionality and requirements to the control circuit for the coupling components to maintain the protective functionality of an automatic switch-off for the coupling components. The advantage of the invention is a significantly better performance over harmonic immunity in the low voltage supply. Furthermore, the higher performance will result in a higher reliability when the switching component is installed in a supply network with a considerable amount of high frequency components on the supply network.

Description

Introduction [0001] The invention relates to current transformer or current transducer (CT) used in Automatic Circuit breakers at low voltage in accordance to the low voltage directive. The current transformers are used for measuring of the current in the main paths L1, L2, L3 & N. Besides that the current transformer delivers energy to the trip unit implemented in the automatic circuit breaker.

[0002] The circuit breakers in scope of this innovation are all standard automatic breakers, which are not specially designed, but certified in accordance with the low voltage directive. In addition the circuit breakers applied in the invention include the functionality of an undervoltage release (UVR) and / or electronic trip unit for tripping of the breaker. The tripping functionality is not part of the invention, as this is already known technology as described in ex. IPR US8587149 B2.with one or more poles. Besides that the circuit breaker can be of any kind of Vacuum breakers, Air Circuit Breakers, Molded Case Circuit Breakers, Miniature Circuit Breakers and Load breakers.

[0003] It' well known to use the current transformers (CTs) in circuit breakers, but up until now these CTs have for the main paths of current L1, L2 and L3 been implemented with two independent coils: 1. Rogowski coil or hall element for measuring of currents in the main current path L1, L2, L3,

N, PE 2. Energy coil for generating energy to the trip unit. The energy is transformed via the three main phases, L1, L2, and L3.

[0004] As the CTs are designed to operate at the natural frequency of the circuit in which they are implemented, the CTs are vulnerable and weak against higher frequencies including harmonics. The typical natural frequency of the grid network could be 50Hz/60Hz/200Hz/400Hz, but can in general be of any kind of frequency.

[0005] The presence of harmonics are getting more and more typical in numerous applications involving converters, motor drives, switched power supplies etc. In all switched power networks the issues with higher frequencies disturbances and harmonics will be more and more significant.

[0006] As the purpose of the energy transformer is to deliver energy at the natural frequency, the performance is optimized for this frequency. This approach have the side affect that higher frequencies wifi cause higher loses in the energy transformer, which will be transferred to heat loses [0007] It’s the scope of this invention to simplify the CT by removing the energy transformer for improved performance against higher frequencies generated by switching devices in the grid, but still keep the functionality and protection capabilities of an automatic circuit breaker. The invention relates to a circuit breaker as specified in the introductory part of claim 1 and that is further characterized by the features specified in the second part of the claim. The invention is further characterized by the features of the dependent claims.

Detailed description

Figure overview * Figure 1 > This figure provides a genera! sketch and overview of a traditional d||rent transducer or CT consisting of both an energy coil and measurement coil. * Figure 2. This figure proved a general sketch of a Current transducer or CT without energy coil. The Current transducer or CT oniy consists of a measurement coil. * Figure 3. This figure is a schematic providing the interfaces and components used in-order to maintain a tripping functionality in case of missing Aux. supply for the circuit breaker [0008] In applications using switched network in low voltage power circuits the voltage and current will always be affected by the switching in the low voitage power circuit.

[0009] The switching of the power circuits are typically performed by switching the three phases L1, L2 and L3 using a PWM (Pulse Width Modulation) signal in order to meet a specific power level. The switching frequency is depended on application and / or power ievel required.

[0010] The principal in the switching device is to switch the main phases L1, L2 and L3 at a higher frequency than the natura! frequency of the grid. The switching frequency can in principai be of any frequencies between 0 Hz- infinity.

[0011] it’s inevitable that the switching will affect the THD {Total Harmonics Distortion) level of the power delivered from the switching circuit. The voitage / current waveform hence will consist of two frequency components: 1-.- The natural frequency of the grid in which the switch device operates and 2. The switching frequency and all the harmonics related to the natural frequency and the switching frequency.

[0012] The presence of higher frequencies than the natural frequency of the network will affect the performance of the components used in the network, as these are typical designed for usage at the natural frequency of the network.

[0013] For Circuit Breakers, which can be of any kind of Vacuum breakers, Air Circuit Breakers, Molded Case Circuit Breakers, Miniature Circuit Breakers, Load breakers the currents are typically measured by the usage of a CT (Current Transducer or Current Transformer).

[0014] The CT for the circuit breakers consists of several parts. The housing for the components [1] is typically made of a type of molded plastic. The inside of the housing [1] can either by free air or filled with mold material. The Rogowski current transformer [2] transforms the main current from the busbar [7] with any kind of scaling to a measuring current for the trip unit through the cables [6]. The energy transformer [3] consists of a primary winding, which is coupled around the main current busbar [7], the core [3] + [4] for improving flux density at the natural frequency at low voltage Ex. 50Hz/60Hz/200Hz/400Hz. The secondary winding is connected to the trip unit through cables [5] for energy supply to the electronic trip unit. The energy transformer [3] and the core [3] + [4] are designed for the usage at the natural frequency of the network in which the circuit breaker is mounted Ex. 50Hz/60Hz/200Hz/400Hz.

[0015] As the purpose of the energy transformer is to deliver energy at the natural frequency, the performance is optimized for this frequency. This approach have the side affect that higher frequencies will causes higher loses in the energy transformer, which will be transferred to heat loses.

[0016] The invention will remove the energy transformer [3] + [4], as these are the parts which causes the increased heat loses. The Trip Unit [12] can be either self powered with energy from the energy transformer or powered using an external power supply.

[0017] The invention will be based on the solution of using an external power supply and not support the usage of the self powered application.

[0018] In order to make sure that the protection functionality of the circuit breaker is intact at a power failure of the external power supply for the Trip Unit [12], the invention make use of four different solutions for power and/or voltage monitoring of the power supply for the Trip Unit. 1. The Trip Unit [12] has a dedicated internal sensor circuitry for monitoring the aux. power supply lines [10], which is similar to monitor the Trip Unit Supply. 2. The circuit breaker have two UVR (Under Voltage Release) [13] + [14] implemented, where one of these are dedicated for monitoring of the aux. power supply for the circuit breaker. 3. A relay or contactor is incorporated in the auxiliary monitor circuitry for the circuit breaker.

The relay or contactor [16] is wired to the power supply for the Trip Unit [12]. 4. A voltage monitoring device [17] and/or current monitoring device [18] is incorporated in the monitor circuitry for the circuit breaker. The monitoring device is wired to the power supply for the Trip Unit [12].

[0019] Description of case 1. The internal circuitry for monitoring of the auxiliary power supply for the Trip Unit [12] is either coupled to the tripping, device, which is indicated by a tripping coil [15] independently or connected together with the trip signals implemented in the Trip Unit. In all cases the monitoring circuitry trips the circuit breaker in case the supply is below the range of proper operation of the Trip Unit [12], The monitoring of the auxiliary supply can be of voltage, current or power consumption. The monitoring circuitry sends a signal to the tripping device, in this example a tripping coil [15], which makes the circuit breaker trip in case of an undervoltage and/or undercurrent and/or low power consumption of the auxiliary power supply for the Trip Unit. The tripping device will interact with the main shaft, which includes the main contact set. In case of a trip the main contact set for L1, L2, L3 and N will be opened via the interaction between the tripping coil and the main shaft.

[0020] Description of case 2. The tripping of the circuit breaker in case of failure at the auxiliary power supply for the Trip Unit is in this case realized by using a UVR [13] + [14]. If the circuit breaker is only mounted with one UVR, the UVR [13] should be wired to the power supply lines [8] for Trip Unit [12]. The limitation is in this case that the UVR [13] needs to operate in the same voltage rating as the Trip Unit. To overcome this, a second UVR [14] could be used. If the circuit breaker is implemented with two UVR’s [13] + [14], one UVR [13] could be rated for the same voltage rating as the voltage rating for the Trip Unit [12], and wired to the power supply lines [8] + [10] for the Trip Unit. The other UVR [14] could be used at any voltage ratings available for the UVR. In case of an undervoltage case at the auxiliary supply the UVR will trip the circuit breaker. The UVR will interact with the main shaft, which includes the main contact set. In case of an undervoltage at the UVR the main contact set for L1, L2, L3 and N will be opened via the interaction between the UVR and the main shaft.

[0021] Description of case 3. The tripping of the circuit breaker in case of failure at the auxiliary power supply [10] is in this case by using an interface relay or contactor [16] in combination with an UVR [14]. If the circuit breaker is only mounted with one UVR [14], and the application requires an UVR with a different voltage rating than the Trip Unit [12] the usage of an interface relay or contactor [16] is needed. The coil of the interface relay or contactor [16] is wired to the auxiliary power supply line [10] for the Trip Unit [12], For the purpose of tripping in case of undervoltage at the auxiliary supply, it doesn’t matter whether the coil is wired to the positive or the negative pole for the power supply [10]. In case of an undervoltage at the auxiliary supply, the coil connected to the auxiliary supply will be de-energized and the contact set of the external relay or contactor [16] will open, which will de-energize the UVR [14] and trip the circuit breaker. The UVR will interact with the main shaft, which includes the main contact set. In case of an undervoltage at the UVR the main contact set for L1, L2, L3 and N will be opened via the interaction between the UVR and the main shaft.

[0022] Description of case 4. The tripping of the circuit breakers in case of failure at the auxiliary power supply [10] is in this case done by internal and/or external monitoring of the auxiliary power supply. The monitoring can either be done by usage of a voltage monitoring device [17] and/or a current monitoring device [18]. In case of an undervoltage of the auxiliary power supply for the Trip Unit [10], the voltage monitoring device opens the contact set of the voltage monitoring device [17], which will de-energize the UVR [14] and trip the breaker. In case of an undervoltage of the auxiliary power supply for the Trip Unit [10], the current monitoring device opens the contact set of the current monitoring device [17], as the current flow will lower than expected, which is set to a threshold value. The open contacts set will de-energize the UVR [14] and trip the breaker. The UVR will interact with the main shaft, which includes the main contact set. In case of an undervoltage at the UVR the main contact set for L1, L2, L3 and N will be opened via the interaction between the UVR and the main shaft.

[0023] The above mentioned four options can either be implemented as stand-alone options, or one or more options can be implemented at once. Regardless of how many options are implemented at once the invention will ensure that the protection functionality of the breaker is intact, and therefore the circuit breaker can be categorized as either switch disconnector, which is a non-automatic breaker or categorized as an automatic circuit breaker.

[0024] The enhancement of removing the energy transformer from the CT will be significantly increase in performance for harmonics performance in switched network compared to the traditional CT with both energy and Rogowski transducer. The increased performance is obtained be removing the lossy part of the combined current transformer.

Claims (8)

1. Circuit breaker provided from external aux. trip unit supply consisting of trip unit and / or undervoltage coil (UVR), characterized by consisting of current transducers without energy transducer and being able to measure aux. the trip unit supply and disconnects the main circuit of L1, L2, L3 and N in the event of failure of supply connections to the trip unit. Aux supply 2 is defined as aux. the supply to the generic UVR where the supply can be any arbitrary voltage, depending on the requirements of the UVR. Monitoring of supply connections to the trip unit (aux. Supply) is provided by the following options: a. Current monitoring [17] by aux. the connection using any device for monitoring and signaling the power consumption of the trip device to the circuit breaker. In the event of either under-consumption or over-consumption of the current in relation to a given threshold value for the trip unit, the power monitoring unit will interrupt the aux. supply 2 the supply to the generic UVR, which will cause the circuit breaker to trip. b. Voltage monitoring [18] of aux. the connection with the use of any device for monitoring and signaling the voltage level of the trip device to the circuit breaker. In case of either undervoltage or overvoltage in relation to a given threshold value of the trip unit voltage level, the voltage monitor will interrupt the aux. supply 2 the supply to the generic UVR, which will cause the circuit breaker to trip. c. Calculation of power consumption in aux. supply when calculating power consumption based on the voltage level and current consumption in aux. compound. In case of either underconsumption or overconsumption of the power in relation to a given threshold value for the power consumption precede the unit, the monitoring unit [17] and / or [18] used will interrupt the aux. supply 2 supply to the generic UVR, which will cause the circuit breaker to trip d. Monitoring the aux. supply to the circuit breaker using a transfer relay [16], which monitors and signals the availability of supply voltage to the trip unit. In case of undervoltage, the relay will interrupt the aux. supply 2 the supply to the generic UVR, which will cause the circuit breaker to trip. For electronic monitoring circuits implemented in the trip unit [12], the monitoring circuit will monitor any of the following parameters: e. Current monitoring of aux. the supply [10]. If the power consumption in aux. if the supply for the circuit breaker is above or below a defined threshold value for the circuit breaker, the monitoring circuit will trip the breaker using the trip coil and / or switch aux. 2 the supply for the generic UVR. Either case will cause the circuit breaker to trip. f. Voltage monitoring of the auxiliary supply [10]. If the voltage level of aux. if the supply [10] is above or below a given defined threshold for the circuit breaker, the monitoring circuit will trip the breaker using the trip coil and / or switch aux. 2 the supply for the generic UVR. Either case will cause the circuit breaker to trip. g. Power monitoring of aux. supply [10], If power consumption for aux. if the supply [10] is above or below a given defined threshold for the circuit breaker, the monitoring circuit will trip the breaker using the trip coil and / or switch aux. 2 the supply for the generic UVR. Either case will cause the circuit breaker to trip. 2. A circuit breaker according to claim 1 comprising at least one current transducer characterized by comprising only one transducer for measuring current in the main circuit. 3. Circuit breaker according to claims 1 and 2 which uses devices for monitoring current and / or voltage and / or power consumption characterized by either specific devices such as amps, voltages, power meters, transfer relays or internal implemented circuits. for monitoring and signaling of amps, volts, power for aux. the supply circuit breaker. 4. Circuit breaker according to any previously mentioned claim comprising a trip unit characterized by using an external auxiliary power supply. 5. Circuit breaker According to any previously mentioned requirement consisting of at least one UVR which is characterized by activating the trip coil in the circuit breaker in case of undervoltage. 6. Circuit breaker according to any previously mentioned claim characterized by controlling an external transfer relay and / or contactor for disconnecting the supply to UVR. 7. Circuit breaker according to any of the preceding claims characterized by using an external voltage monitoring device to disconnect the supply to the UVR. 8. A circuit breaker according to any of the preceding claims, characterized by using an external power monitoring unit to disconnect the supply to the UVR.