The ISIS Neutron and Muon Source Facility, part of UKRI’s Science and Technology Facilities Council, are looking to procure a replacement three-phase Alternating Current (AC) Magnet Power Supply System to make up the losses in a resonant magnet circuit. The requirement is for a modular 1200 kVA three-phase AC voltage source power supply that includes a control system capable of regulating the designated magnet load current to a given setpoint and to a high level of stability. It is important to emphasise that the magnet load current to be regulated is not the same as the AC power supply output current and the measurement signal for the load current will be provided by the facility in the form of a DCCT with a -10/+10 V signal representative of the load circuit current. The three-phase output shall have a variable voltage output from 0 V to 250 V line-neutral and an output voltage accuracy of ±50 mV. The system shall be fed from a nominal 400 Vrms AC, 3-phase 50 Hz sinusoidal supply, intrinsically safe by design, with high efficiency, high reliability, high maintainability and fully compliant and marked with relevant standards.