A liquid resistor is an electrical

resistor A resistor is a passive two-terminal electronic component that implements electrical resistance as a circuit element. In electronic circuits, resistors are used to reduce current flow, adjust signal levels, to divide voltages, bias active e ...

in which the resistive element is a

solution Solution may refer to: * Solution (chemistry), a mixture where one substance is dissolved in another * Solution (equation), in mathematics ** Numerical solution, in numerical analysis, approximate solutions within specified error bounds * Solu ...

. Fixed-value liquid resistors are typically used where very high power dissipation is required. They are used in the rotor circuits of large

slip ring A slip ring is an electromechanical device that allows the transmission of Electric power, power and electrical Signal, signals from a stationary to a rotating structure. A slip ring can be used in any Electromechanics, electromechanical system ...

induction motor An induction motor or asynchronous motor is an AC motor, AC electric motor in which the electric current in the rotor (electric), rotor that produces torque is obtained by electromagnetic induction from the magnetic field of the stator winding ...

s to control starting current, torque and to limit large electrical fault currents (while other protection systems operate to clear or isolate the fault). They typically have

electrode An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or a gas). In electrochemical cells, electrodes are essential parts that can consist of a varie ...

s made of welded steel plate (

galvanised Galvanization ( also spelled galvanisation) is the process of applying a protective zinc coating to steel or iron, to prevent rusting. The most common method is hot-dip galvanizing, in which the parts are coated by submerging them in a bath o ...

to reduce corrosion), suspended by insulated connections in a conductive chemical solution held in a tank - which may be open or enclosed. The tank body is normally solidly grounded or earthed. A typical unit can be rated for continuous use, or for short periods when used for current limitation in protection systems.

Liquid neutral earthing resistor

A common use in the electrical power generating and distribution industry is as a fault current limiter in the common neutral leg of large three-phase transformers and generators. In the UK they are known as Liquid Neutral Earthing Resistors (LNERs). A rating of 0.5 megawatt for 30 seconds would not be unusual to protect the winding of a 660 MW generator. In this application where a neutral leg current flows due to a current imbalance between the generator or transformer windings due to a fault, it is limited in magnitude by the resistor. A permanently installed

current transformer A current transformer (CT) is a type of transformer that reduces or multiplies alternating current (AC), producing a current in its secondary which is proportional to the current in its primary. Current transformers, along with voltage or poten ...

(CT) fixed around the neutral leg feeder to the LNER senses the current. The CT sends a signal current to an external sensing circuit (the protection system) which then sends a signal to the relevant circuit breaker to open and disconnect the supply or isolate the generator (or transformer) from the fault. The ohmic value of the resistor is calculated as a function of the permissible fault current and the system voltage to earth.A.C. Franklin, D.P.Franklin et al (1983) The J&P Transformer Book 11th ed.P484: Butterworth & Co Ltd.

Electrolyte in power industry LNERs

The

electrolyte An electrolyte is a substance that conducts electricity through the movement of ions, but not through the movement of electrons. This includes most soluble Salt (chemistry), salts, acids, and Base (chemistry), bases, dissolved in a polar solven ...

is normally

sodium carbonate Sodium carbonate (also known as washing soda, soda ash, sal soda, and soda crystals) is the inorganic compound with the formula and its various hydrates. All forms are white, odourless, water-soluble salts that yield alkaline solutions in water ...

(soda ash) and/or

sodium bicarbonate Sodium bicarbonate ( IUPAC name: sodium hydrogencarbonate), commonly known as baking soda or bicarbonate of soda (or simply “bicarb” especially in the UK) is a chemical compound with the formula NaHCO3. It is a salt composed of a sodium cat ...

(baking soda). This salt solution is

alkaline In chemistry, an alkali (; from the Arabic word , ) is a basic salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in water. A solution of a soluble base has a pH greater than 7.0. The ...

and electrode corrosion effects on

galvanised steel Hot-dip galvanization is a form of galvanization. It is the process of coating iron and steel with zinc, which alloys with the surface of the base metal when immersing the metal in a bath of molten zinc at a temperature of around . When expos ...

tanks is manageable if re-galvanisation is possible. The resistance of the bulk electrolyte is a function of temperature and the concentration of the saltG.R. Jones, M.A. Laughton, M.G. Say (1993) Electrical Engineer's Reference Book / edited P2/7: Reed Educational and Professional Publishing. . governed by the formula: :''R''_''θ'' = {{sfrac, ''R''₀, 1 + 0.03''θ'' where ''θ'' is the temperature (in Celsius) and ''R''₀ is the standardised or datum calibration temperature. A specialised technique is required to accurately calibrate an LNER electrolyte bulk resistance value and it is normally carried out by experienced power engineers and technicians. This task must be done off-load at routine intervals (roughly 2–4 years depending on results from routine monitoring) to maintain the resistance value within tolerance and facilitate inspection of the LNER.

References

Electric power Resistive components

Liquid neutral earthing resistor

Electrolyte in power industry LNERs

See also

References