![Current Transformer (CT)
Substation Secondary Design Course | Eng Ahmed Metwally
Introduction to
By [F05] Team:
Amal Nasr | Mohamed Kamal | Salah Alfiky | Hassan El Sawy | Ahmed Tamer](https://image.slidesharecdn.com/currenttransformer-250623091810-24cef5a3/85/Introduction-to-Current-Transformer-Substation-1-320.jpg)
Introduction to Current Transformer (Substation)
- 1. Current Transformer (CT) Substation Secondary Design Course | Eng Ahmed Metwally Introduction to By [F05] Team: Amal Nasr | Mohamed Kamal | Salah Alfiky | Hassan El Sawy | Ahmed Tamer
- 2. Agenda 01 Introduction 02 Types 03 Key Manufacturers 10/29/2024 Current Transformer (CT) 2 04 Parameters 05 Notes
- 3. Introduction & Description How current transformers work Electromagnetic Induction: • When an alternating current flows through the primary winding (the conductor), it generates a magnetic field around the conductor. • This changing magnetic field induces a current in the secondary winding according to Faraday’s Law of Electromagnetic Induction, which states that a change in magnetic flux through a circuit induces an electromotive force (EMF) in that circuit.
- 4. Introduction & Description How current transformers work • A CT requires good accuracy around the nominal current value. • The metering instruments do not need to withstand currents as high as the protection relays • Current transformers are used to supply information to the protective relays • ratio • burden • accuracy class They are defined by:
- 5. Introduction & Description How current transformers work Current Transformation: The relationship between the primary current (𝐼𝑝) and the secondary current (𝐼𝑠 ) is defined by the turns ratio (𝑁) of the transformer: Ip Is = Ns Np Ns: number of turns in the secondary winding Np: number of turns in the primary winding. For example, in a 1000:1 CT, 1000 A in the primary results in 1 A in the secondary.
- 6. Introduction & Description How current transformers work Single-ratio CTs Standard single-ratio CTs that are manufactured in the United States are as listed:
- 7. Introduction & Description How current transformers work Multi-ratio CTs • Single primary winding and a tapped secondary winding as shown: • The standard multi-ratio CTs that are are listed:
- 8. Components Key components Core: 1) Material: laminated silicon steel to reduce eddy current losses, or ferrite for high-frequency applications. 2) Types: a) Toroidal Core: Circular shape, used for high accuracy and low burden. b) Bar Core: Used for large conductors, where the bar passes through the core. 2. Windings: 1) Primary Winding: Usually consists of a single turn (the conductor itself) or a few turns for higher current applications 2) Secondary Winding: Multiple turns are wound around the core to step down the current
- 9. Components Key components 3. Insulation: 1) Materials: a) Resin: Used in encapsulated CTs for moisture resistance. b) Oil: Provides cooling and insulation in larger CTs. 2) Housing: Purpose: Protects the internal components from environmental factors. Mounting Options: CTs can be mounted on switchgear, busbars, or distribution panels.
- 10. Types & Uses Uses 1 Measurement - Energy Meters - Power Quality Monitoring 2 Protection - Provides information to the protection relay Examples Used in all substation in the HV and MV switchgears
- 11. Types & Uses Types Current transformers (CTs) are categorized based on their design, application, and construction. Each type serves specific purposes in electrical systems, particularly in measurement and protection, tailored for specific applications and installation requirements. They are extensively used in protective relaying, energy measurement, and monitoring within power systems, ensuring the safe and accurate assessment of electrical currents in high-voltage environments.
- 12. Types & Uses Types 1. Wound Current Transformer A CT that has a primary winding consisting of one or more turns mechanically encircling the core or cores. The primary and secondary windings are insulated from each other and from the cores and are assembled as an integral structure (C57.13). Voltage level: High Voltage (HV) Usage: Indoor
- 13. Types & Uses Types 1. Wound Current Transformer •Description: A wound current transformer is a transformer with separate primary and secondary windings wrapped around a laminated core. It’s located on the high-voltage side of substations. The primary winding consists of one or more turns of large cross-section wire connected in series with the circuit to be measured. •Application: Commonly used in applications where high accuracy is required, such as in metering and protection in substations. •Characteristics: • Accuracy: High accuracy over a wide range of currents. • Voltage Rating: Can handle high voltages, making them suitable for high-power applications.
- 14. Types & Uses Types 2. Toroidal (or Ring) Current Transformer •Description: A toroidal CT features a doughnut-shaped core through which the primary conductor passes. The secondary winding is wound around the core. •Application: Often used in energy monitoring systems and industrial applications due to their compact design. •Characteristics: • Ease of Installation. • Compact Size: Smaller and lighter compared to other types. • Noise: Produces less noise. • Power Efficiency & Electromagnetic Shielding. Voltage level: Medium Voltage (MV) and Low Voltage (LV) Usage: Indoor or Outdoor
- 15. Types & Uses Types 3. Split-Core Current Transformer •Description: A unique design that allows the core to be opened and closed around a conductor without interrupting the circuit. •Application: Widely used in energy auditing, monitoring, and retrofitting applications. •Characteristics: • Flexibility: Ideal for applications where access to conductors is limited. • Portability: Lightweight and easy to transport. Voltage level: Medium Voltage (MV) and Low Voltage (LV) Usage: Indoor (typically)
- 16. Types & Uses Types 4. Bar-Type Current Transformer It’s a special type of window current transformer with a solid bar placed permanently through the window. It has a fixed, insulated straight conductor in the form of a bar, rod, or tube that is a single primary turn passing through the magnetic circuit and that is assembled to the secondary, core, and winding (C57.13) Voltage level: Medium Voltage (MV) Usage: Indoor
- 17. Types & Uses Types 4. Bar-Type Current Transformer •Description: The primary conductor is integrated into the transformer design , while the secondary part consists of windings wound on a circular core surrounding the primary bar conductor. It’s typically used in switchgear. •Application: Commonly found in high-current applications, such as in substations and industrial distribution boards. •Characteristics: • High Current Handling: Can withstand stresses of heavy overcurrent. • Cost: Costly compared to the wound-type counterparts but give extremely accurate results.
- 18. Types & Uses Types 5. Window-Type Current Transformer A CT that features an open window through which a single conductor passes. The magnetic field generated by the conductor induces current in the secondary winding. It’s very similar to a bushing type CT. Voltage level: Medium Voltage (MV) and Low Voltage (LV) Usage: Indoors or Outdoors
- 19. Types & Uses Types 5. Window-Type Current Transformer •Description: It has a secondary winding insulated from and permanently assembled on the core but has no primary winding as an integral part of the structure. •Application: Suitable for retrofitting and monitoring existing installations. •Characteristics: • Ease of Use: Simple to install without modifying the existing circuitry. • Versatility: Compatible with various conductor sizes.
- 20. Types & Uses Types 6. Bushing Current Transformer A BCT is a window-type current transformer mounted around the bushing’s flange. It may be inside the main tank of an oil circuit breaker or mounted externally. It consists only of a toroidal-shaped core with a secondary winding. The bushing’s center conductor forms the single turn primary of the BCT (doesn’t have a traditional primary winding). Voltage level: High Voltage (HV) Usage: Outdoor
- 21. Types & Uses Types 6. Bushing Current Transformer •Description: Integrated within the bushing of high-voltage equipment, such as transformers and circuit breakers. It features a primary winding around the conductor passing through the bushing and a secondary winding encapsulated within the bushing. •Application: Used in substations and high-voltage systems for current measurement and protection. •Characteristics: • Compact Design: Space-efficient and seamlessly integrates with existing equipment. • High Voltage Capability: Designed to handle high-voltage levels. • Durability: Built to withstand harsh environmental conditions. • Safety: Provides electrical isolation for safe operation.
- 22. Types & Uses Types 7. Optical Current Transformer (OCT) • Principle: Optical current transformers (OCTs) use fiber optic technology to measure current based on the Faraday effect for current measurement. • Advantages: • Electromagnetic Interference Immunity: Making them ideal for high-voltage environments where noise can affect accuracy. • High Electrical Isolation: For safety in high-voltage applications. • High Speed Measurements • Wide Bandwidth: For accurate high-frequency signal measurement. • Lightweight and Easier to Install: Compared to traditional CTs.
- 23. Types & Uses Types 7. Optical Current Transformer (OCT) • Applications: Ideal for substations, renewable energy systems, and smart grids. • Limitations: Generally, more expensive and may require specialized handling. • Standards: Governed by IEC and IEEE standards to ensure safety and performance. Voltage level: High Voltage (HV) and Medium Voltage (MV) Usage: Outdoor (typically)
- 24. Types & Uses Broader category Current sensors • Definition: This broader category includes various devices that measure current, including but not limited to CTs. Current sensors are devices that measure the flow of electric current in a conductor. They can provide information about both alternating current (AC) and direct current (DC) levels. Relationship Between Current Sensors and Current Transformers • Subset: CT is a specific type of current sensor designed primarily for AC measurements, particularly in high-power applications, and external power supply isn't needed. Whereas current sensor is a generalized concept, that can detect both AC and DC (transforms AC into DC or DC into DC) and external power supply is needed. • Measurement Principle: CTs rely on electromagnetic induction, while other current sensors may use different principles such as the Hall effect or resistive measurements. • Applications: Both CTs and other current sensors can be used in similar applications, such as energy monitoring, protection, and metering.
- 25. Key Manufacturers Top Manufacturers 1. ABB ❑ Overview: A global leader in power and automation technologies with a diverse portfolio. ❑ Products: 1. Types of CTs: Indoor and outdoor CTs, metering CTs, protection CTs. 2. Notable Product: ABB’s "Transformer Protection CT", designed for high accuracy in protection applications. ❑ Location: Zurich, Switzerland. CT30/250, Split-core current transformer used to transform primary currents to 5A
- 26. Key Manufacturers Top Manufacturers 2. Siemens: ❑ Overview: A major player in electrical engineering with a focus on innovation. ❑ Products: 1. Types of CTs: Ring core CTs, encapsulated CTs for harsh environments. 2. Notable Product: Siemens’ “SENTRON". ❑ Location: Munich, Germany. SENTRON CT 1200/5 A 10 VA CL 0.5, Bushing-type cuurent transformer
- 27. Key Manufacturers Top Manufacturers 3. Schneider Electric ❑ Overview: Focuses on smart and sustainable energy solutions. ❑ Products: 1. Types of CTs: Smart CTs integrated with IoT technology for remote monitoring. 2. Notable Product: Schneider’s "PowerLogic" series for energy management. ❑ Location: Rueil-Malmaison, France. PowerLogic CT 150/5A, Split-core current transformer
- 28. Key Manufacturers Top Manufacturers 4. General Electric (GE) ❑ Overview: Known for high-quality electrical equipment and advanced technology. ❑ Products: 1. Types of CTs: Protective CTs, measuring CTs for different voltage levels. 2. Notable Product: GE “OSKF" CTs designed for grid solutions. ❑ Location: Boston, Massachusetts, USA. Oil-Insulated Current Transformers 72.5 kV to 800 kV, up to 5000A
- 29. Key Manufacturers Top Manufacturers 5. Eaton ❑ Overview: Provides power management solutions across various sectors. ❑ Products: 1. Types of CTs: Precision CTs for metering and protective applications. 2. Notable Product: Eaton’s “T-Line" CTs known for excellent performance. ❑ Location: Dublin, Ireland. T-Line, Current transformer HF8A, 2500A/5A, Class 0.2S
- 30. Parameters Rated Primary Current Ipr Shall be selected according to the load current and to make sure CT do not reach saturation Rated Secondary Current Isr Typically, 1A or 5A this is according to: - CT burden - Distance between relay and CT Burden Impedance of secondary circuit usually expressed in VA (Isr 2 Rb) at specific power factor Rb: rated resistive burden Rct: secondary winding resistance 10/29/2024 Current Transformer (CT) 30
- 31. Parameters Extended Current Rating (%) Expressed as a percentage of the rated current (e.g., 120%, 150%, 200%), elucidates the CT’s ability to handle higher currents while maintaining temperature limits 10/29/2024 Current Transformer (CT) 31
- 32. Parameters Rated Short-time Thermal Current Ith Maximum current the CT shall withstand for a specific short time typically 1-3 seconds Rated Dynamic Current Idyn Maximum peak value the CT shall withstand without being mechanically damaged Used to address the electromagnetic forces resulting from a short circuit 10/29/2024 Current Transformer (CT) 32
- 33. Parameters Highest voltage for equipment Um (r.m.s.) Highest voltage during normal operation and shall be at least equal to the system voltage Rated power-frequency withstand voltage Ud (r.m.s.) A typical 50/60Hz waveform for 60 seconds Rated lightning impulse withstand voltage Up (peak) A standard high voltage testing waveform characterized by a fast-rising edge Um < Ud < Up 10/29/2024 Current Transformer (CT) 33
- 34. Parameters 10/29/2024 Current Transformer (CT) 34 IEC 61869-1
- 35. Parameters Protection Cores Example: 5P20 P: Accuracy class designation 5: Composite error, ±5% 20: Accuracy limit factor (ALF) this means that up to x20 the rated current, the composite error will be sustained, and the core will not saturate There are other types of classes used for distance and differential protection and transient performance 10/29/2024 Current Transformer (CT) 35
- 36. Parameters Metering Cores Examples: 0.1 – 0.2 – 0.2s – 0.5 – 0.5s – 1 – 3 – 5 The number above is ratio error At these values burden can be 25-100% of rated output For 3 and 5 burden is 50-100% Instrument Security Factor (ISF) Examples FS5 and FS10 A multiple value of the primary current at which the CT will saturate to prevent damage 10/29/2024 Current Transformer (CT) 36
- 37. Parameters Insulation Classes Maximum continuous use temperature in degrees Celsius 10/29/2024 Current Transformer (CT) 37 Letter Designation Thermal Class °C Y 90 A 105 E 120 B 130 F 155 H 180 N 200 R 220 IEC 60085-2007 Table 1 – Thermal class assignment
- 38. Parameters Nameplate Example 10/29/2024 Current Transformer (CT) 38
- 39. IEEE Std C57.13-2016 Accuracy class mean at 100% rated current the error=0.3% and at 10% rated current error =0.6% (double). Example: 0.3B-0.9
- 40. IEEE Std C57.13-2016 cont.. Metering class related to burden impedance. The accuracy class is the description of how much voltage the transformer can supply to the output circuit(burden),without the CT core going into saturation. C200,C400
- 41. What Is Knee Point According To IEEE Std C57.13-2016 1. CT secondary voltage depend on the primary current. 2. When the secondary voltage exceed the knee voltage the CT become saturated which means there is no current produce in secondary winding or there is distorted current that lead to malfunction operation of protective relay.
- 42. What Is Knee Point According To IEC 61869-2 -IEC value is higher than IEEE, IEEE is more conservative
- 43. Compare between IEEE & IEC Standard. Compare between IEEE & IEC class. Compare between IEC &IEEE polarity symbol.
- 44. Saudi Electricity Company standard (SEC Standard) TSP: Transmission Service Provider TES: Transmission Engineering Standard. TMSS: Transmission Material Standards and Specification.
- 45. CT Class From TES-P-119.28 Note: if class PX is specify it shall be preferred over class P measuring current transformers, the accuracy class is designated by the highest permissible percentage of the ratio error (ε) at rated primary current and rated output.
- 46. Design Parameter & Equation From TES-P-119.28
- 47. Core & Insulation Material From 50-TMSS-01
- 48. Specification From Egyptian Distribution Material Specification (EDMS).
- 49. Notes 10/29/2024 Current Transformer (CT) 49 • Why Should the CT Secondary Never be Opened? counter balancing flux. Ø = Ø 1 - Ø 2 ,is the flux that flows through the core. Its value is relatively small If compared to Ø 1. This flux maintains linear relationship between secondary and primary current depending on the core material when secondary connected with Load.
- 50. Notes 10/29/2024 Current Transformer (CT) 50 High Voltage Risk: potentially harmful voltages that can cause electric shock or damage equipment. Insulation Breakdown: high voltage produced can exceed the insulation ratings of the transformer leading to insulation breakdown & possible arcing,fire hazards. Equipment Damage: The excessive voltage can damage the CT itself and any connected devices, such as meters or relays. Safety Hazards: If someone is working on the system &inadvertently opens the secondary circuit, they may be exposed to dangerous conditions. Protective measures that rely on the CT's proper functioning may fail.
- 51. Notes 10/29/2024 Current Transformer (CT) 51 • Why is the polarity of a current transformer (CT) is crucial? High voltage current transformer (HVCT) polarity refers to the orientation of the transformer’s primary and secondary windings and how they relate to the direction of current flow.
- 52. Notes 10/29/2024 Current Transformer (CT) 52 • Why is the polarity of a current transformer (CT) is crucial?
- 53. Notes 10/29/2024 Current Transformer (CT) 53 • Why is the polarity of a current transformer (CT) is crucial? • Accurate Measurement: If the CT is connected with the wrong polarity, the readings can be reversed or inaccurate, leading to erroneous data. • Protection Systems: Incorrect polarity can cause relays to trip when they shouldn’t or fail to trip when needed, compromising system safety. • System Coordination: In multi-CT setups, maintaining proper polarity ensures that all devices operate in harmony. This is vital for coordination between different protection devices and ensuring that faults are accurately detected and isolated. • Phase Relationships: Accurate phase alignment is important for power quality and system performance. • Safety: Incorrectly connected CTs can lead to dangerous situations, such as those involving high voltage surges when the secondary circuit is open.
- 54. Notes 10/29/2024 Current Transformer (CT) 54 What is the Dual Ratio Current Transformer ? Current transformers having a center tapped secondary. it is necessary to have available two ratios of primary to secondary current from the same secondary winding of the CT.
- 55. Notes 10/29/2024 Current Transformer (CT) 55 • What is the Dual Ratio Current Transformer ? • The ratio obtained by the tap is usually one-half the ratio obtained by the full secondary winding. • With 200 amperes flowing in the primary, CT. They are used in applications where a connection 1S1 – 1S2 will produce 5 amperes out of the secondary. • Then as the load grows to 400 amperes, the secondary circuit will be reconnected to 1S1 – 1S3 to produce 5 amperes in the secondary. • It is not recommended to reconnect while the unit is energized, the secondary terminals must be short circuited so as not to induce high voltage in the secondary circuit. • On a dual ratio tapped secondary CT, both the full winding and the tapped winding cannot be operated simultaneously. • Another design of CT commonly used is the double secondary CT. Where the CT has two cores, two secondary windings and one common primary winding.