Description
Product Overview
The Alstom CDG34 is a triple-pole non-directional IDMT (Inverse Definite Minimum Time) over-current and earth-fault protection relay designed for industrial power protection applications. It builds upon the rugged and well‐proven CDG family of Alstom’s electromechanical relays, providing protection using either three over-current elements or a combination of two over-current plus one earth-fault element. The CDG34 relay ensures selective and reliable fault clearance in distribution feeders, transformers, or generators under variable load and fault conditions.
Featuring an “extremely inverse” time/current characteristic, the CDG34 relay enhances coordination among upstream and downstream protective devices by adjusting trip time based on fault magnitude, while maintaining a definite minimum time under maximum faults. Its robust electromechanical construction, simple and durable mechanism, and self-powered operation (in many variants) make CDG34 a preferred choice where reliability, simplicity, and longevity are vital. The Alstom CDG34 is specially suited for installations where environmental conditions are harsh, auxiliary power supply may be unreliable, and maintenance must be minimized.
In systems where selectivity, coordination, and dependable fault detection are required—such as in power distribution boards, switchgear, or substation protection—the CDG34 plays a central role. With its triple-pole design (horizontal or vertical mount versions) and flexible configuration (3 overcurrent, or 2 overcurrent + 1 earth-fault), the Alstom CDG34 relay supports a variety of protection schemes. High torque, low overshoot, good accuracy, mechanical indication (flags), and robust case design add value, making the CDG34 an asset in any protection scheme demanding high reliability.
Technical Specifications
| Parameter Name | Parameter Value |
|---|---|
| Product Model | CDG34 (tripole/non-directional overcurrent ± earth fault) |
| Manufacturer | Alstom (formerly GE/Alstom protection relays) |
| Product Type | Electromechanical Protection Relay (IDMT O/C & E/F) |
| Pole / Elements Configuration | 3-pole; either 3 O/C elements or 2 O/C + 1 E/F element |
| Time Characteristic | Extremely inverse time/current curve with definite minimum time |
| Current Setting Range | Varies by variant; typical overcurrent tap settings cover multiple ranges (e.g. 0.5-10 A in some versions) |
| CT Secondary Rating | Commonly 1 A or 5 A depending on field / model variant |
| Burden | Approx. 3 VA per element under rated currents in many standard versions |
| Case Size & Mounting | Standard 3D horizontal or vertical mounting; flush panel mounting style |
| Contact Configuration | Typically 2 N/O self-resetting (S/R) contacts per element; auxiliary or high reset variants available |
| Operating Frequency | 50 Hz standard (some variants may support 60 Hz in specific markets) |
| Insulation / Dielectric Withstand | Withstands ~2.5 kV AC RMS (50 Hz) for one second between circuits and case; lower rating (1.25 kV AC) between open contacts in certain models |
| Mechanical Features | Visible trip flag/indicator; robust disc mechanism; adjustable time multiplier scale |
Main Features and Advantages
High selectivity and coordination: The Alstom CDG34 excels at coordinated fault clearing due to its extremely inverse time characteristic, which ensures that higher fault currents result in faster tripping, whereas minor overloads allow longer delay. This feature helps reduce nuisance tripping and maintains continuity under moderate load imbalances.
Flexible protection configuration: Depending on system requirements, CDG34 may be configured with three overcurrent elements, or two overcurrent plus a central earth-fault element. This flexibility enables tailoring of protection schemes to include earth fault detection without needing a separate relay, which simplifies wiring and reduces panel space.
Self-powered elements: Many versions of CDG34 operate without need for external auxiliary power, especially for basic overcurrent and earth-fault elements. This ensures protection remains functional even if auxiliary power fails, increasing system resilience.
Robust mechanical construction: The disc‐type mechanism has high torque, low overshoot, and visible mechanical indicators (flags) which provide immediate visual confirmation of operation. The case is designed to be durable, with standard 3D horizontal or vertical configurations, suited for harsh environments, vibration, and tropical conditions.
Low burden and high accuracy: The burden (VA) on CTs is kept low, which helps reduce loading on CT secondaries and preserves accuracy. Accuracy classes conform to standards, ensuring consistent trip timing under varying ambient conditions.
Ease of maintenance: The CDG34’s simple electromechanical design means fewer failure points, easy servicing of contact parts or flag indicators, and minimal calibration effort. Replacement parts are straightforward and accessible.
Application Field
The Alstom CDG34 is widely used in protection of electrical power distribution systems in industrial plants, utilities, and infrastructure. In power distribution feeders, the CDG34 monitors the current in each phase (and optionally earth faults), ensuring that overcurrents or ground leakage faults are cleared before damage occurs to cables or equipment.
In transformer protection, the CDG34 serves as backup protection for transformer windings or as feeder protection downstream of transformers, especially in environments where harmonics, fluctuating load, or unbalanced loading are common. Its triple-pole design allows symmetrical or asymmetrical current protection depending on system layout.
In sectors such as petrochemical, manufacturing, mining, or water treatment, where reliability is critical and maintenance windows limited, the CDG34 offers durability and self-powered operation that minimize dependence on auxiliary supplies. It is also used in switchgear, both indoor and outdoor, where ambient temperature, humidity, dust, or vibration may challenge more fragile electronic devices.
Utilities and substations often use CDG34 in time-graded protection schemes, coordinating with upstream fuses or circuit breakers, to ensure selectivity so that only the nearest upstream device isolates fault, preserving service elsewhere. This is essential in networks with multiple feeders, mesh grids, or ring mains.
Installation and Maintenance
Pre-installation preparation: Before installing CDG34, ensure that the relay panel or switchgear has been completely de-energized and proven safe. Confirm that current transformers feeding the relay have correct secondary ratings (1 A or 5 A depending on the variant), proper polarity, and minimal lead resistance. Inspect the panel cut-out to match the case size (3D horizontal or vertical mounting) and ensure that the flush mounting is possible. Check that ambient conditions (temperature, humidity, vibration) comply with relay specifications. Make sure wiring for overcurrent and earth-fault circuits is properly sized, shielded as applicable, and that mechanical trip flags will be visible.
Maintenance recommendations: Periodically inspect the CDG34 relay for dust, corrosion, or buildup on terminals and contacts. Clean external surfaces and ensure ventilation if applicable. Operate or simulate trip under test conditions to verify proper functioning of overcurrent and earth-fault elements, including verifying time-delay settings and flag indicators. Check contact resistance and inspect the disc mechanism for free movement and minimal friction. Tighten all electrical connections and inspect insulation condition around wiring. If ambient temperature or frequency differs from standard, verify that timing curves are still valid.
Replacement of worn parts (contacts, flag springs) should be done with genuine components, and after replacement, re-test the relay’s characteristic curves. Keep log records of any trips or malfunctions to detect trends. Calibration (if needed) should be performed using test sets and matching actual current and time settings to specified curves.
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