CDG31 ALSTOM

Description

Detailed parameter table

Product introduction

In the critical domain of electrical power protection, the Alstom CDG31 asserts itself as a stalwart electromechanical relay from Alstom’s legacy CDG series, engineered for inverse definite minimum time (IDMT) overcurrent and earth fault safeguarding in medium-voltage distribution networks. This versatile unit combines independent overcurrent and earth fault elements within a single drawout case, utilizing induction disc mechanisms to deliver precise, repeatable tripping based on IEC or BS 142 curves. Positioned as a foundational component in the CDG lineup, the Alstom CDG31 targets applications requiring robust, non-directional protection without digital complexities, making it a reliable sentinel for feeders and transformers where simplicity meets unyielding performance. Its essence in automation frameworks revolves around instantaneous fault isolation, interfacing with circuit breakers to avert cascading failures and preserve grid stability.

The Alstom CDG31‘s core capabilities encompass configurable tap settings for sensitivity tuning—from 0.5 to 2.5 times rated current for phase faults and down to 0.1 for sensitive earth detection—coupled with a 0.1 to 2.5 time multiplier for adaptive coordination. Housed in a tropicalized, dust-tight enclosure, it supports heavy-duty contacts rated for 5 A at 250 VAC, ensuring secure signaling to SCADA or annunciators. Within broader protective relaying schemes, the Alstom CDG31 enhances system resilience by minimizing nuisance trips through harmonic restraint and instantaneous high-set elements, while its low-burden design (under 3 VA) integrates effortlessly with existing CTs, slashing retrofit costs.

Moreover, the Alstom CDG31 encapsulates Alstom’s heritage in proven electromechanical design, now stewarded by GE Grid Solutions, offering field-proven longevity with mechanical flags for post-event analysis. By prioritizing deterministic response over programmable features, it equips utility engineers with a straightforward tool for zonal protection, fostering safer, more efficient power delivery in an era of evolving grid demands.

Core advantages and technical highlights

The Alstom CDG31 leverages functional ingenuity through its dual-disc architecture, where the overcurrent unit employs a damped induction mechanism for IDMT characteristics identical across all taps, eliminating the need for curve recalibration during adjustments. This ensures consistent protection grading, with earth fault sensitivity extending to 10% of phase settings for detecting high-impedance ground faults in compensated networks. An optional instantaneous high-set element trips in <20 ms at 10 times pickup, augmenting selectivity in meshed systems, while mechanical interlocks prevent inadvertent resets, streamlining operator workflows in substations.

Performance reliability hallmarks the Alstom CDG31, operating across 50/60 Hz with a reset ratio of 0.95 for overcurrent and 0.85 for earth fault, guaranteeing no chatter under marginal conditions. Its trip time adheres strictly to IEC 60255 curves—10 seconds at twice setting with TMS=1—while tolerating 150% continuous overload without degradation, ideal for motor starting inrush. The low 1-3 VA burden preserves CT accuracy over long runs, and auxiliary supply independence (self-powered from CTs) bolsters deployment in remote feeders, where voltage dips under 80% nominal sustain full functionality.

Durability defines the Alstom CDG31‘s ethos, with a tropicalized finish resisting humidity up to 95% and temperatures from -10 to 55 °C, per IEC 60068-2 testing for vibration (2 g) and shock (20 g). Sealed drawout case achieves IP52 ingress protection, shielding against dust and arcs, while heavy-duty contacts endure 10^6 operations at 5 A inductive loads, certified to IEC 61810-1. These traits yield an MTBF exceeding 200,000 hours, curtailing maintenance in harsh utility environments.

Compatibility anchors the Alstom CDG31 in legacy and hybrid setups, with standard 4TE or 7TE case footprints mating to MiCOM series for phased migrations, and binary I/O syncing with IEC 61850 gateways. It accommodates CT secondaries from 1 to 5 A, and optional watchdogs signal internal failures via NO/NC pairs.

Ease of deployment elevates the Alstom CDG31, featuring plug-in drawout for live testing without outages, and color-coded tap plugs for visual settings verification. Front-panel flags and test blocks facilitate commissioning in under an hour, with no software required—empowering field crews to achieve precise coordination using handheld calculators, thus bridging generational expertise in protective relaying.

Typical application scenarios

In rural distribution feeders, the Alstom CDG31 guards against phase-to-phase faults in overhead lines spanning 11 kV, where its IDMT curve coordinates with upstream 132 kV breakers to clear downed conductors in 0.5 seconds at 5 times load current amid lightning-prone monsoons. Under variable agricultural loads with harmonic distortions from inverters, the relay’s restraint feature suppresses false trips, meeting rural electrification mandates by isolating only affected sections—reducing outage durations from hours to minutes and preserving revenue for utilities serving remote hamlets.

Substation transformer banks deploy the Alstom CDG31 for restricted earth fault protection, monitoring neutral CTs to detect winding shorts at sensitivities below 20% In during 33/11 kV step-downs under urban thermal cycling. Its low-burden design integrates with existing delta-wye configurations without CT upgrades, addressing operators’ needs for rapid isolation—evidenced by <50 ms trips on internal arcs, compliant with IEEE C37.91, that avert oil fires and extend asset life by 15% through minimized thermal stress in densely loaded grids.

Industrial motor control centers harness the Alstom CDG31 for backup overcurrent in 6.6 kV starters, where earth fault elements safeguard against ground insulation failures in petrochemical pumps amid corrosive atmospheres. The relay’s tropicalization withstands 40 °C humidity, enabling setpoint tweaks via taps for inrush discrimination—fulfilling safety engineers’ IEC 60255 adherence while curbing downtime, as coordinated grading with fuses prevents nuisance shutdowns during startup surges, optimizing continuous processes like refining that demand 99.5% availability.

Related model recommendations

• CDG11: Single overcurrent unit in the CDG series, serving as a simplified feeder protector complementary to the Alstom CDG31 for applications needing phase-only monitoring without earth fault integration.
• CDG61: Three overcurrent elements variant, acting as an expanded counterpart to the Alstom CDG31 for multi-phase selectivity in ring main units requiring independent directional grading.
• CDG21: Combined overcurrent and earth fault with definite time, functioning as a faster-acting alternative to the Alstom CDG31 in zones demanding hybrid IDMT/DMT curves for urban substations.
• MiCOM P12x: Numerical successor series, recommended as a digital upgrade from the Alstom CDG31 offering programmable logic while retaining curve compatibility for modern SCADA ties.
• CDG34: Directional overcurrent model, pairing with the Alstom CDG31 in parallel feeders to enhance selectivity against reverse power flows in meshed networks.
• VAGM22: Auxiliary metering relay accessory, enhancing the Alstom CDG31 with voltage supervision for under/over detection in combined protection schemes.
• CAG14: Sensitive earth fault disc unit, integrable with the Alstom CDG31 for augmented ground detection in Petersen coil-earthed systems.

Installation, commissioning and maintenance instructions

Installation preparation

Prior to integrating the Alstom CDG31, evaluate the switchgear bay for compliance with IEC 62271: maintain -10 to 55 °C ambient, <95% RH noncondensing, and seismic anchoring for 0.5 g accelerations to ensure disc alignment integrity. Compile a toolkit with 5 mm hex drivers torqued to 1.5 Nm for case latches, insulated CT leads (2.5 mm²), and a 500 V megger for insulation checks; confirm auxiliary supply at 110/220 VAC/DC with <10% ripple via dedicated fuses. Vital safeguards include de-energizing bays under LOTO, verifying CT polarity with phase rotation meters, and applying anti-corrosive grease to terminals—prioritizing arc-flash PPE to amplify safety, while pre-marking drawout positions hastens alignment and cuts exposure in live-access panels.

Maintenance suggestions

Routine stewardship of the Alstom CDG31 entails quarterly flag inspections for latent trips and secondary injection tests with ramp currents to affirm pickup accuracy within 5%, preempting drift in CT-burdened circuits. Diagnostics via test blocks isolate disc adhesions—remedied by gentle demagnetization coils or tap recalibration—while logbook entries track operate times against IEC curves for trending. For overhauls post-10 years, extract the drawout unit, clean induction cups with lint-free swabs, and reseal contacts with dielectric grease; procure OEM discs and springs to confine swaps to 45 minutes under shadow testing. Annual thermography on terminations and vibration audits in generator bays perpetuate precision, crafting a vigilance protocol that extends the Alstom CDG31‘s duty cycle beyond 25 years via informed, interval-based renewals.

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