DK201400213A1

DK201400213A1 - Current Transducer without energy coil for circuit breakers

Info

Publication number: DK201400213A1
Application number: DK201400213A
Authority: DK
Inventors: John Larsen
Original assignee: Siemens Aktieselskab
Priority date: 2014-04-14
Filing date: 2014-04-14
Publication date: 2015-11-02
Also published as: DK178815B1

Abstract

The scope of the invention is to make a more simple construction of the current transducer currently used widely in circuit breakers for application within the scope of low voltage directive. The invention removes the energy coil from the current transducer and adds additional features and requirements to control circuit in order to keep the protective functionality of an automatic circuit breaker. The benetit of the solution is a highly improved performance with respect to harmonics and higher frequency in the low voltage grid. The higher performance will in addition yield a higher rel iability when the circuit breaker is mounted into a grid environment with high frequency pollution.

Description

intrisduiClioo [0001] The invention relates to current transformer or current transducer fCT) used in Automatic Circuit breakers at low voltage in accordance to the low voltage directive, 1ECS043S. The current transformers are used for measuring of the current in the main paths Li, L2 and 13 as well as delivering energy to the trip unit implemented in the automatic circuit breaker. [0002] The circuit breakers in scope for this invention are automatic circuit breakers that are certified in accordance with the low voltage directive IEG80439 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 13 been implemented with two independent coils. 1. Rogowski coil or haii element for measuring of currents in the main current path L1,12, L3, N, RE 2. Energy coii for generating energy to the trip unit. The energy is transformed via the three main phases, LI. 12, 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/SOHs/200Rz/4GOHz, but can in general 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 ail switched power networks the issues with higher frequencies disturbances and harmonics will be more and more significant.

[0008] As the purpose of the energy-transformer is to deliver energy at the natural frequency, the performance is optimised for this frequency. This approach have the side affect that higher frequencies will cause higher loses in the energy transformer, which wili 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 gnd, but stiii keep the functionality and protection capabilities of an automatic circuit breaker.

Detailed description

[0008] In applications using switched network in low voltage power circuits the voltage and current wili always be affected by the switching in the low voltage power circuit

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

[0010] The principal in the switching device is to switch the main phases L1, L2 and L3 at a higher frequency than the natural frequency of the grid The switching frequency can in principal fee of any frequencies between 0 Hz ~ infinity. [0011] it’s inevitable that the switching will affect the THD (Totai Harmonics Distortion) level of the power delivered from the switching circuit The voltage / current waveform hence wiii consist of two frequency components: 1:, The natural frequency of the grid in which the switch device operates and I; 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 wilf 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 Rcgowski 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 [?], the core [3] * |4| for improving flux density at the natural frequency at low voltage Ex, S0Hz/6OHs/2OOHz/4OOHz: 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. 6OHz/6OHz/2O0HaMQ0Hz.

[00 55] 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 wiii 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 die Trip Unit: [12], the invention make use of th ree 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 power supply.

2, The circuit breaker have two UVR (Under Voltage Release) [13] + [14] implemented, where one of these are dedicated for monitoring of the power supply for the Trip Unit 3. An external relay or contactor is incorporated in the external control circuitry for the circuit breaker. The external relay or contactor [18] is wired to the power supply for the Trip Unit [12], 4 An externa! voltage monitoring device [17] and/or current monitoring device [18} is incorporated In the externa! control circuitry for the circuit breaker. The externa! 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 coil [15j independently or connected together with the tnp signals implemented in the Trip Unit. In ali 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 coii [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. [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 [12f. The limitation is m this case that the UVR [13] needs to operate in the same voitage rating as the Trip Unit. To overcome this, a second UVR [14] couid be used, if the circuit breaker is implemented with two UVR's [13J + [14], one UVR [13] could be rated for the same voitage rating as the voitage rating for the Trip Unit [12], and wired to the power supply fines [8] + [10] for the Trip Unit The other UVR [14] could be used at any voltage ratings available for the UVR.

[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 external relay or contactor [15] in combination with an UVR [14], lithe circuit breaker is only mounted with one UVR [14], and the application requires an UVR with a different voitage rating than the Trip Unit [12] the usage of an externa! reiay or contactor [18] is needed. The coii of the externa! reiay or contactor [16] is wired to the auxiliary power supply line [10] for the Trip Unit [1:2], For the purpose of tripping in case of undervoltage at the auxiliary supply, it doesn't matter whether the obi! 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 externa! relay or contactor [18] wÉ open, which wiif de-energise the UVR [14] and trip the breaker.

[0022] Description of case 4. The topping of the circuit breakers in case of failure at the auxiliary power supply [10] Is in this case done by externa! 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 undervoiiage of the auxiliary power supply for the Tnp Unit [10]. the voltage monitoring device opens the contact set of the voltage monitoring device [1 ?], which will de-energize the UVR [14] and trip the breaker, in case of an undervoitage 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 deenergize the UVR [141 and trip the breaker. [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 he 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

2. Circuit breaker according to claim | compromising of at least one Current Transducer that is characterized by only containing a transducer for measuring the current in the main path.
3. Circuit breaker according to claim1 and 2 compromising of a Trip Unit that is characterized by only using an externa! auxiliary power suppiy.
4. Circuit breaker according to previous claims compromising of at least one UVRihaf is charaeterizedby energizing the trip coil in the circuit breaker in case of an underyoitage.
5. Circuit breaker according to previous claims that is characterized by the capability to monitor the auxiliary suppiy voltage.
6. Circuit breaker according ίο previous claims that is characterized by using an external relay and/or contactor for disconnection of power supply io the UVR,
7. Circuit breaker according to previous claims that is characterized fey using an external voltage monitor unit for disconnection of power suppiy to the UVR