STAMFORD S5 Low Voltage Alternator 450-750 kVA

Mid-size power for 500 to 750 kVA generator sets

The STAMFORD S5 is the S-Range alternator for sets between roughly 500 and 750 kVA at 50 Hz and up to 937 kVA at 60 Hz. It serves the gap between the S4 and the large S6 frame and is a common choice for data-room standby sets, industrial plant and prime-power containers where a single engine drives a 600 to 700 kVA alternator.

It is a four-pole, wire-wound brushless machine with single-bearing construction, IP23 enclosure and class H insulation. The brochure highlights simplified interfaces, easy reconnectability, enhanced thermal management through CoreCooling, high-efficiency airflow, and two new core lengths at 700 and 750 kVA. An adaptor foot option lets a set base switch between S5 and S6, a flexible foot option allows a switch between alternator brands, and the brochure adds S5 Special ratings. Its general-arrangement drawing is indicative of the S5-H core, and additional voltages are available through STAMFORD applications engineering.

Technical specifications

S5 Dedicated ratings, 400 V, 50 Hz, class H 125/40 (winding 311)

At 480 V, 60 Hz the same models range from 594 kVA (C4) to 937 kVA (H4) in the continuous column. The brochure notes the ratings were preliminary at publication, so confirm them at order stage.

Specifying an S5 for a prime or standby set

Because the S5 covers six core lengths in about 250 kVA of range, the step between models is small, from 30 to 60 kVA at 400 V. Match the alternator to the engine kW rather than to the set name, and decide early whether the set must be reconnectable for another voltage, because reconnection is a build option rather than something added later.

Options worth deciding up front

A PMG-excited MX341 or MX321 gives better short-circuit support and isolates the AVR from non-linear load distortion, which matters for UPS and rectifier loads. The self-excited AS440 is the lower-cost route for plain standby. Ask for the quadrature droop kit when the set will parallel with other sets, and for winding RTDs or thermistors if the controller will monitor stator temperature. Other factory build options are an anti-condensation heater with terminal box, bearing RTD, air inlet filter, remote voltage trimmer, RFI suppressor kit, excitation loss module and diode failure detector.

How the STAMFORD S5 alternator works

The STAMFORD S5 is a four-pole brushless alternator. A small exciter on the shaft makes the field current for the main rotor, so there are no brushes or slip rings. The AVR senses the output voltage and adjusts the exciter field to hold the voltage steady. The AS440 is self-excited, and the MX341 or MX321 can be used with a PMG for more motor starting power. The single bearing design bolts to the engine flywheel with an SAE 1 adaptor. CoreCooling and the airflow design keep the windings cool.

Where the STAMFORD S5 is used

• Data room standby sets
• Industrial plant with a 500 to 750 kVA demand
• Prime-power container sets
• Commercial buildings and hospitals
• Sites with paralleled generator sets

Selection checklist for the STAMFORD S5

• Rating in kVA at 50 Hz or 60 Hz
• Voltage in the 380 to 480 V range
• Model from S5L1D-C4 to S5L1D-H4
• Duty: prime or standby
• AVR: AS440, MX341 or MX321
• PMG option for motor starting
• Winding RTDs or thermistors
• Anti-condensation heater

Installation, commissioning and maintenance notes for STAMFORD S5

Match the SAE adaptor and the coupling to the engine flywheel and align the set with care. Connect the twelve terminals for the voltage needed. Run the set unloaded and check voltage and frequency, then apply load in steps. Keep the air path clean and dry, because the IP23 enclosure is not made for wet locations, and fit the heater where the set stands idle in damp air.

Requesting a quotation for the STAMFORD S5

Please send the kVA, the voltage, the frequency, the duty and the engine details. Seven Star LLC serves industrial customers in Oman and the GCC and replies with a quotation based on the information provided.

STAMFORD S5 ratings

At 400 V and 50 Hz the six models are 450, 455, 461, 467, 470 and 475 kVA in the continuous 125/40 column. The brochure ratings were preliminary at publication.

STAMFORD S5 construction

It has four poles, wire-wound construction, insulation class H and IP23 protection. It can be reconnected for 3-phase use.

STAMFORD S5 foot options

An adaptor foot lets a set base switch between S5 and S6 frames, and a flexible foot allows a change of alternator brand.

STAMFORD S5 voltage and winding

The voltage range is 380 to 480 V, and other voltages go through applications engineering.

Alternator records for STAMFORD S5

Keep the nameplate data, the insulation resistance readings and the load test results in the set file.

Choosing the right STAMFORD S5 model

Choose the model from the engine kW at the generator frequency, then check the motor starting need before choosing the AVR.

Documents and quotation

Seven Star LLC supplies STAMFORD S5 alternators on request. Provide kVA, voltage, frequency, engine and SAE housing, AVR choice and duty. Related components sit under Diesel Generator Spare Parts, and a finished set in this size class is the Cummins 312/315 kVA diesel generator set. Check the final winding and rating data in your quotation before ordering.