Abbreviations and Definitions
This post summarizes and explains some of the most commonly used abbreviations and definitons from the field of variable frequency drives (VFD), drive systems and associated areas, such as power electronics, harmonics and power quality, monitoring, testing…
AFE
Active Front End
Grid side converter (in drives often called “rectifier” although this is not 100% correct for regenerative applications) consisting of active power semiconductor switches. AFE often supports bi-directional power flow or adjustment of the power factor.
ASD
Adjustable Speed Drive
– A term for power electronic based elecric drive, frequently used in North America. A synonym of Variable Frequency Drive (VFD).
BIL
Basic Insulation Level
Term describing the insulation level from withstand voltage point of view. The insulation level of equipment may be characterized e.g. by lightning impulse withstand voltage (‘LI’) and short duration power frequency withstand voltage (‘AC’).
CSI
Current Source Inverter
VFD technology with main reactor in the dc link (dc side) that provides the inverter with a current source character. Low and medium power CSIs supply asynchronous machines. LCI is a special type of CSI used in combination with synchronous machines in high power range.
DFE
Diode Front End
Grid side converter (rectifier) consisting of diodes only. DFE converter allows just uni-directional power flow and the power factor cannot be actively controlled.
DGA
Dissolved Gas Analysis
DGA is a method to monitor the transformer condition throughout its lifetime and to provide an insight into the severity of fault based on the composition of dissolved gases within the sample of insulating liquid. DGA may be part of transformer preventive maintenance plan.
DSP
Digital Signal Processor
DSP is a fast specialized processor optimized for digital signal processing. It is used in various applications such as telecommunications, consumer electronic, mobile phones or power electronic.
DTC
Direct Torque Control
Method to control the torque of inverter-fed electric machine. DTC is based on hysteresis controllers maintaining the torque and flux in a specified band. The method is known for its superior dynamic performance.
DTL
Direct To Line
VFD topology that allows direct connection of the VFD to the supply grid without the need of isolation transformer. It is typically available only for specific grid voltage(s) matching the product design.
DUT
Device Under Test
DUT refers to the device / equipment / product undergoing specific testing. Another term is equipment under test (EUT) that is basically a synonym. In drive systems the term DUT is often used in conjuction with test benches.
EAF
Earth Fault Monitoring
Protection functionality to detect an earth fault within the drive system and react correspondingly (i.e. issuing alarm or trip signal).
ECD
Equivalent Circuit Diagram
Method to describe an element or system by a set of circuit parameters (R, L, C). The parameters can result from a calculation or can be determined by measurements. ECD is often used to decribe e.g. a transformer or electric motor. The ECD usually has a limited validity (e.g. for a nominal frequency or narrow frequency range only).
EMC
Electromagnetic Compatibility
Ability of electric equipment to properly function within its designed electromagnetic environment. The equipment shall not exceed certain level of electromagnetic emissions (EME) that could cause disturbance or malfunction of other devices. At the same time, the equipment shall be designed for certain level of electromagnetic immunity (EMI).
FAT
Factory Acceptance Test(s)
FAT consists of a series of tests that shall verify the design and functionality of the equipment. FAT typically includes tests defined in the applicable standards (routine, type and special tests in IEC classification). Additional tests mutually agreed between purchaser and manufacturer may be performed as well.
FRA
Frequency Response Analysis
FRA is a method to evaluate the mechanical integrity of core, windings and clamping structures within power transformers by measuring their electrical transfer functions over a wide frequency range (IEC definition). The full name is actually Sweep frequency response analysis (SFRA).
FRT
Fault Ride Through
Performance feature to ride through a grid fault (disturbance) without tripping. In most cases the drive ramps the torque rapidly down to almost zero and waits until the grid voltage recovers. In some cases, especially in generating plants, a reactive current injection may be required to support the grid. A synonym is just a Ride Through (RT).
GTO
Gate Turn-Off (Thyristor)
Self-commutated thyristor, a predecessor of IGCT. It combines the advantages of a thyristor (high current rating, low on-state voltage, high short time overload) with switch-off capability of a power transistor.
HMI
Human Machine Interface
HMI is a user interface that allows the operator to monitor and control the machine and supervise the processes. Modern HMI can be realized in form of in-built screen, computer screen, touchpad etc.
HVDC
High Voltage Direct Current
Power electronic based technology for transmission of electric power. HVDC transmission links are typically used for transmission of large power over long distance. Benefits are reduced losses and increased stability of power system. Back-to-back HVDC arrangement may be used to interconnect asynchronous grids of different fundamental frequency.
IGBT
Insulated Gate Bipolar Transistor
Transistor based power semiconductor widely used in many power electronic converters. Available in low voltage and medium voltage range.
IGCT
Integrated Gate-commutated Thyristor
Self-commutated thyristor-based power semiconductor, an advancement of GTO thyristor. Known for robust design and low conduction losses. Popular in medium voltage VSI applications of medium and high power.
LCI
Load-commutated Inverter
Thyristor based converter technology, especially used in high-power range (multi megawatt rating). It is a special type of current source inverter (CSI) where the grid-side and machine-side converters are commutated by an external voltage. Therefore, LCI is used in combination with eletrically excited synchronous machine.
LI
Lightning Impulse
LI mostly refers to an impulse voltage with standardized waveshape (1.2 μs front time and 50 μs time to half-value) that is used to describe the insulation level of equipment and to test it for design verification purpose (e.g. as part of type testing).
MMC
Modular Multilevel Converter
Modern converter topology consisting of series-connected power cells to reach required voltage. MMC typically features high number of levels in AC-side voltages and therefore high power quality.
MV
Medium Voltage
MV is usually used to describe voltage range from 1 kV AC to 36 kV AC and 1.5 kV DC to 54 kV DC. The exact voltage limits may differ based on specific country or region. Moreover, sSome countries may not use the term ‘medium voltage’ at all.
NPC
Neutral Point Clamped
Popular VSI topology at medium voltage level. Unlike basic 2-level VSI used in low voltage the NPC introduces a third level (3-level NPC) and therefore increasing the power quality. Higher level NPC topologies are derived from the basic 3-level NPC.
PCC
Point of Common Coupling
PCC is a point where the user’s system (e.g. production plant) interfaces the utility electric grid. PCC often has a contractual meaning stating specific performance to be met there, such as harmonic distortion, power factor etc.
PDS
Power Drive System
This is a term used in IEC 61800 series to describe the adjustable speed power electronic based drive system. A synonym term is variable speed drive system (VSDS).
PWM
Pulse Width Modulation
Type of modulation used in converters (inverters) to synthesize an alternating waveform of current or voltage. The pulses all have constant magnitude but variable width. The switching instants are defined by coincidence of a carrier signal with modulation signal. PWM covers many specific variants and sub-variants. The modulation is very popular in AC motor control applications.
SAT
Site Acceptance Test(s)
SAT is test program performed on site. The purpose of SAT is to verify the design, functionality and performance of the equipment or system. SAT is often performed on larger or more complex systems as part of final verification before acceptance from purchaser side.
SFC
Static Frequency Converter
Term used for power electronic based static converter. SFC often refers to power electronic converters used in grid interties (interconnection of three-phase grids with different power frequency or interconnection between three-phase utility grid and single-phase railway grid) but may also be used for VFDs (historically used e.g. for LCI based soft starters).
SSO
Subsynchronous Oscillation
Oscillation in the system at frequency lower than the power frequency. SSO may be caused e.g. by series capacitors without damping control.
SSTI
Subsynchronous Torsional Interaction
Torsional interaction at frequency lower than the power frequency. SSTI may occur e.g. as interaction between synchronous generators in a power generation plant and larger non-linear “consumers” (HVDC terminal, large VFD installation etc).
SVC
Static VAR Compensator
Equipment for static compensation of reactive power (VAR). SVC, in contrast to rotating synchronous condensers, has no significant moving parts. It consists of capacitors and reactors in conjunction with power electronics to provide controllability (often using thyristors). SVC may also include harmonic filter(s) so that t combines two basic functions: reactive power compensaton and harmonic filtering.
THD
Total Harmonic Distortion
Term used in power quality and harmonic standards to express overall harmonic distortion caused by the sum of all individual harmonics. It is defined as the ratio of the sum of powers of all harmonic components to the power of fundamental frequency.
VCB
Vacuum Circuit Breaker
Type of circuit breaker using vacuum as arc extinction medium inside a sealed chamber. VCB is dominant type of circuit breaker in medium voltage installations.
VFD
Variable Frequency Drive
Power electronic based converter for energy-saving speed control of AC electric motors. The term VFD covers the broad family of ‘drives’ such as direct converters (cycloconverters, MMC direct topologies) and indirect converters (CSI and VSI).
VSD
Variable Speed Drive
Equipment to variate the speed of the driven load. it includes VFDs but also other means such as gas and steam turbines, DC motor drives, hydrodynamic (fluid) coupling etc.
VSDS
Variable Speed Drive System
A term describing variable speed electric drive system consiting of key system components such as input isolation transformer, variable frequency drive, electric motor and possibly other system components. More or less an equivalent to power drive system (PDS) defined in IEC.
VSI
Voltage Source Inverter
VFD technology with capacitor bank in the dc link (dc side) that provides the inverter with a voltage source character. Alternative terms are “voltage fed inverter”, “voltage stiff inverter” or “voltage source converter”.
WRIM
Wound Rotor Induction Machine
Induction (asynchronous) machine with wound rotor windings with usually accessible terminals. WRIM is an opposite to squirrel cage rotor construction.
The list of common abbreviations and definitons will be gradually extended. So you may be interested to check this post again in the future and see what is new here. Also, feel free to write us your suggestions.
References
[1] Electropedia: The World’s Online Electrotechnical Vocabulary, https://electropedia.org/
