Cressall Resistors: a hidden hero in electrical engineering

~ How do resistor technologies support power generation, transmission and usage? ~

Cressall Resistors is the world’s foremost resistor manufacturer, offering an unrivalled combination of engineering expertise and the widest range of power resistor technologies in its sector. With facilities in Leicester and Dereham, Cressall was established over 100 years ago and its resistors support electrical and mechanical systems around the world — from energy generation to electric vehicles and equipment testing.

Resistors are fundamental building blocks in electrical circuits. They control the flow of current, dissipating excess electrical energy into heat to ensure the system remains operational. While it might seem like a simple function, the design and construction of high-power resistors is complex. Cressall is specialised in the design and manufacture of resistor technologies built to handle demanding environments, withstanding extreme temperatures, high voltages and heavy currents. This makes them ideal for a wide range of applications, from industrial and offshore settings to the transportation sector.

The rise of renewables

The growing focus on the energy transition means technologies involved in renewable energy generation and transmission have a huge opportunity. An increasing number of renewable sources are required to reach net-zero goals, and many of these are further away from the grid, like offshore windfarms.

These renewable sources are inherently variable, meaning their output fluctuates depending on weather conditions. Resistors play a crucial role in managing this variability and ensuring that the current within the system remains within operational constraints. An example is the use of pre-insertion resistors on wind farms, which keep voltages consistent with minimal dips, reducing disruption and mitigating against temporary overvoltages caused by exceptionally strong winds.

Offshore wind is a particularly promising area. The UK has a world-leading ambition to deploy up to 50GW by 2030, with up to 5GW coming from floating offshore wind.

Offshore wind farms mean that electricity is increasingly being transmitted over long distances, which means using high voltage direct current (HVDC).

However, to make offshore wind’s output compatible with the grid, HVDC converter stations are placed on both ends of the transmission line, converting the AC power generated by offshore wind turbines into DC power for transmission and then back into AC power for grid integration onshore. Cressall’s filter resistors dissipate unwanted harmonic currents as heat to maintain quality and reliability when converting AC to DC after long-distance transmission from offshore wind farms.

The EV revolution

Along a similar thread, the electrification of the automotive market is creating a demand for robust power management solutions. The UK, US and EU will all impose a ban on the sale of new petrol and diesel vehicles from 2035. Before this date, the UK additionally has the zero-emission vehicle (ZEV) mandate, which requires that 28 per cent of new car sales are EVs in 2025, 52 per cent are EVs in 2028 and 80 per cent are pure electric in 2030. Resistors play a crucial role in the EV manufacturing chain, as they support both battery and fuel cell EVs to brake safely.

EVs use a regenerative braking system, which ensures any excess energy produced when a vehicle decelerates is converted back into electrical energy and stored in the battery. This increases EV range and therefore reliability over long distances. Cressall’s EV2 is a dynamic braking resistor (DBR), which is an essential component of an EV regenerative braking system. If the battery is full or there is a failure, the EV2 removes this excess energy from the system to prevent damage.

Testing the limits

Cressall’s expertise extends beyond resistors with its Power Prove division. Power Prove specialises in load banks, which are essentially large, controllable resistors used for testing power generation equipment. These load banks simulate real-world operating conditions, allowing engineers to assess the performance and capacity of generators, transformers and other critical electrical components.

Many critical facilities require an uninterruptible power supply (UPS) to ensure ongoing operations in the event of a mains power disruption. Essentially any application where a power outage would result in serious, negative consequences such as financial losses, compromised safety and disrupted operations needs a UPS. This includes hospitals, airports, data centres, telecoms base stations and many manufacturing facilities.

Load banks enable rigorous testing and commissioning of UPS systems. By simulating different load conditions, load banks ensure that generators, UPS systems, and other power infrastructure operate at their intended capacities when the time comes that they are needed. This testing process identifies potential issues, verifies system performance and validates the readiness of critical environments for emergencies.

As the world transitions towards a more sustainable and electrified future, Cressall Resistors is well-positioned to support these changes. Resistors and load banks will be essential for integrating renewable energy sources, safeguarding power systems and ensuring the stability and reliability of our power grids.