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Brand: STAMFORD
STAMFORD MX342 Automatic Voltage Regulator (AVR) with Current Limiting
Description
Linear under-frequency roll-off and stator current limiting
The STAMFORD MX342 is a two-phase sensed automatic voltage regulator for STAMFORD brushless AC generators. Two features set it apart from the MX341: a linear volts-per-hertz slope that continues down to 18 Hz, and current limiting through an additional CT input for stator current. The STAMFORD AvK part number printed on the datasheet is E000-23422.
The datasheet stresses that a PMG isolates the AVR from non-linear loads and sustains short-circuit current, and that the regulator corrects for load, speed, temperature and power factor changes. Soft start brings voltage up over about 3 seconds.
Technical specifications
| Parameter | Specification |
|---|---|
| STAMFORD-AVK part number | E000-23422 |
| Sensing input (rated speed) | 190-264 V ac max, 1 phase, 2 wire, 50-60 Hz |
| Excitation source | Three-phase PMG, 170-220 V ac, 3 A per phase, 100-120 Hz at rated speed |
| Exciter drive | Up to 120 V dc; 2.7 A steady; 6 A short-term (10 s) |
| Minimum field resistance | 15 ohms |
| Regulation | +/-1% on average sensing (4% engine governing) |
| Temperature drift | 0.03% per degree C after 10 minutes |
| Soft start | 3-second ramp |
| Typical response | 10 ms AVR; 80 ms to 90% field current; 300 ms to 97% volts |
| Under-frequency protection | Set point 59.5 Hz, user adjustable; linear roll-off down to 18 Hz |
| Analogue input | +/-5 V dc max; 1 V for 5% generator volts; 1 k ohm |
| Droop input | 10 ohm burden; 0.07 A for 5% droop at 0 PF; max 0.33 A |
| Current limit input | 27 ohm burden; max sensitivity 0.28 A; max input 0.33 A |
| Over-excitation protection | Set point 75 V dc, 10 s fixed delay |
| Power dissipation | 12 W maximum |
| Environment | Operating -40 to +70 C; humidity 95% non-condensing; storage -55 to +80 C |
Stability selection and controls
A four-position stability switch sets damping by machine size: position 0 below 90 kW, 1 from 90 to 550 kW, 2 from 550 to 2000 kW and 3 above 2000 kW. Trimmers are VOLTS, STABILITY, UFRO, DROOP, VTRIM, EXC TRIP and I LIM. The current-limit CT must sit in the same phase position as the droop CT, as the datasheet notes.
Where the MX342 differs from the MX341
The MX342 uses similar sensing and PMG supply ranges to the MX341, but its under-frequency roll-off is linear down to 18 Hz, and it adds a current limit input (with an additional CT) for stator current. Choose it only where the alternator wiring diagram calls for this regulator, because it is not a drop-in change from other types.
Fitting precautions
Set VOLTS fully anti-clockwise before the first run, keep the hand trimmer terminals ungrounded, and use only floating, 500 V ac insulated devices on the analogue input. Do not raise voltage above the rating plate figure. The datasheet also notes that the AVR has a droop CT input for parallel running, that uncontrolled excitation is limited by an internal shutdown latched until the generator stops, and that the over-excitation trip is 75 V dc after a fixed 10 second delay.
Documents and quotation
Seven Star LLC supplies STAMFORD MX342 regulators on request. The datasheet is attached. Send the alternator model and serial number plus the code on the old board. See Diesel Generator Spare Parts for related parts or the Cummins C275D5 275 kVA diesel generator set for a complete set. Confirm the version before ordering.
Environmental limits in the datasheet are vibration of 50 mm/s from 20 to 100 Hz and 3.3 g from 100 Hz to 2 kHz, operating temperature from -40 to +70 degrees C, storage from -55 to +80 degrees C, and humidity to 95 percent non-condensing. The unit dissipates 12 W at most.
Datasheets & Documents
- Datasheet STAMFORD MX342 AVR specification, installation and adjustments (EN) Download
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About brand
STAMFORD is the alternator brand of Cummins Generator Technologies, sold together with AvK as STAMFORD | AvK. Its history starts in 1904 with the Cutting Brothers' electrical engineering business in Stamford, England, later renamed Stamford Electrical. Newage Engineers bought Stamford Electrical in 1950, and Cummins took over Newage with Onan in 1986.
Seven Star LLC, an independent supplier in Muscat, sources these alternators and regulators for generator builders and plant owners in Oman and the GCC.
STAMFORD company profile
| Founded | 1904, Stamford, England, by the Cutting Brothers |
|---|---|
| Ownership | Cummins Inc., through Cummins Generator Technologies |
| Sister brand | AvK, founded in Frankfurt in 1919 as A. van Kaick |
| Range | Brushless AC alternators from 7.5 to 11,200 kVA |
| Product families | STAMFORD low and medium voltage alternators, AvK alternators for large and medium voltage sets, automatic voltage regulators such as MX341, MX321 and DM110, spare parts |
Milestones
- 1904: The Cutting Brothers start their business in Stamford.
- 1925: The company is renamed Stamford Electrical.
- 1950: Newage Engineers acquires Stamford Electrical.
- 1986: Cummins acquires Onan and with it Newage.
- 2006: The business is renamed Cummins Generator Technologies.
Alternators and AVRs listed here
The pages cover the S-Range alternators S0, S1, S4, S5, S6, S7K and S9LV, the UC22 and UC27 frames, and the AS480, MX321, MX341, MX342, SX460 and DM110 voltage regulators. Each page carries the ratings and specification from the maker brochure, datasheet or owner manual, including options as printed.
Where these alternators are used
The maker names data centres, marine, telecoms, standby and critical protection, combined heat and power, rail and prime power as typical applications, on diesel and gas engines. In the Gulf these are the same standby and prime-power sets used on camps, plants and pumping stations.
STAMFORD products we list
Ordering parts and alternators: what we need
For an alternator, send the model, serial number, winding number, kVA, voltage and frequency from the nameplate. For a regulator, send the code printed on the existing board and the alternator model, because the right replacement depends on the excitation system.
Facts checked against the STAMFORD | AvK heritage timeline and Grace's Guide, October 2026.
Related products
Frequently Asked Questions
What is special about the MX342?
Linear volts-per-hertz roll-off down to 18 Hz and a stator current limit input.
What is its part number?
The datasheet prints STAMFORD-AVK part number E000-23422.
How is it powered?
From a three-phase PMG, 170 to 220 V ac maximum.
What output current does it provide?
2.7 A continuous and 6 A intermittent for 10 seconds.
How is the stability set?
A four-position switch: below 90 kW, 90 to 550 kW, 550 to 2000 kW and above 2000 kW.
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