When specifying switchgear for a 35kV substation, one of the earliest decisions a project engineer faces is whether to use truck type switchgear or fixed type switchgear. The choice affects not only the capital cost of the equipment, but the long-term operational cost, maintenance schedule, and personnel safety of the entire installation.
This guide breaks down the real differences between the two configurations, compares them across six practical criteria, and gives you a 30-second decision table so you can identify the right choice for your project before you contact a supplier.
What Is Truck Type Switchgear?
Truck type switchgear - also called withdrawable switchgear - is a medium voltage panel in which the circuit breaker is mounted on a wheeled carriage (the "truck") that can be physically moved between three defined positions: Service, Test, and Isolated.
In the Service position, the breaker is fully engaged with the busbar and cable circuits and ready for normal operation. In the Test position, the primary circuits are disconnected, but the secondary control wiring remains connected, allowing protection relays and control functions to be tested without de-energising the busbar. In the Isolated position, the truck is fully withdrawn from the panel and can be removed entirely for inspection or replacement.
This three-position mechanism is the defining characteristic of withdrawable switchgear, and it is the reason why the configuration is the dominant choice for 35kV substations serving power plants, industrial facilities, and utility distribution networks where continuous operation is a priority.
In the context of armored designs such as the KYN61-40.5, the withdrawable truck sits inside a fully segregated breaker compartment bounded by grounded metallic barriers. These barriers separate the breaker compartment from the busbar compartment, cable compartment, and low-voltage control zone, containing any fault energy within a single compartment and preventing arc propagation across the panel. This is the structural principle behind armored switchgear: compartmentalisation enforced by metallic enclosures, not just insulation.
KYN61-40.5 truck-type switchgear internal structure showing withdrawable breaker compartment
What Is Fixed Type Switchgear?
Fixed type switchgear - sometimes called stationary type - has the circuit breaker bolted directly to the primary circuit without a withdrawable mechanism. The breaker cannot be moved to a test or isolated position independently; to carry out any maintenance work on the breaker itself, the entire busbar section must be de-energised and earthed first.
Fixed type panels are simpler in mechanical construction, which means lower initial cost and reduced mechanical complexity. They are a viable choice for installations where planned outages are operationally acceptable and where the switchgear will operate for extended periods without requiring breaker-level maintenance.
Common applications include secondary distribution at lower voltage levels, smaller industrial premises with a single incoming feeder, and installations in locations where the cost premium of a withdrawable design cannot be justified by the operational uptime requirements.
Six-Criteria Comparison: Truck Type vs Fixed Type
1. Maintenance Downtime
This is where the two configurations diverge most sharply. With truck type switchgear, the circuit breaker can be racked out to the isolated position and removed for inspection or replacement while the busbar remains live. Only the one feeder served by that panel needs to be switched off. With fixed type switchgear, every breaker maintenance event requires a full section outage - affecting all feeders on that busbar segment.
For a 35kV substation feeding a continuous industrial process or a utility network with no redundant supply path, the cost of an unplanned or extended outage will rapidly exceed the price difference between the two configurations.
2. Capital Cost
Fixed type switchgear carries a lower initial price. The absence of the withdrawable truck mechanism, position interlocks, and secondary isolating contacts reduces manufacturing cost and panel depth. For budget-constrained projects where outage flexibility is genuinely not required, this represents a legitimate saving.
Truck type switchgear costs more upfront. The withdrawable mechanism, position interlock system, and secondary isolating plug assembly add both material cost and manufacturing precision requirements. However, when total cost of ownership over a 20–30 year asset life is calculated - factoring in planned outage costs, production losses, and the labour cost of extended maintenance shutdowns - the withdrawable design frequently delivers lower lifetime cost.
3. Personnel Safety
Both configurations, when correctly designed and maintained, meet the safety requirements of IEC 62271 and related standards. However, the withdrawable switchgear configuration provides a structural safety advantage: the ability to move the breaker to the isolated position with visible air gaps confirmed before any work begins. This reduces reliance on procedural controls alone and provides a physical barrier between the operative and the energised busbar.
The armored compartmentalisation of designs such as the KYN61-40.5 adds a further layer of protection. Even if an internal arc fault occurs during operation, the grounded metallic barriers contain the fault energy within the affected compartment and vent it through dedicated pressure relief channels - limiting damage to the rest of the lineup and protecting personnel in the switchroom.
4. Space Requirements
Truck type switchgear panels are deeper than their fixed type equivalents, because the withdrawable mechanism requires space for the truck travel path and the maintenance aisle in front of the panel must accommodate the racked-out truck. For the KYN61-40.5, the foundation drawing specifies a minimum front clearance of 3000 mm and a rear clearance of at least 1400 mm.
Fixed type panels can be installed in tighter spaces. If the switchroom footprint is genuinely constrained and cannot be enlarged, this may be a deciding factor.
5. Operational Flexibility
Withdrawable switchgear supports a wider range of operational scenarios. Breakers can be swapped between panels of the same type if a unit fails, a spare breaker truck can be kept on-site and deployed within hours, and protection relays can be tested under load conditions without service interruption. Over the operational life of a substation, this flexibility has measurable value.
Fixed type switchgear offers none of these options. Breaker replacement requires an outage, and in-service relay testing is limited to what can be carried out without withdrawing the breaker.
6. Suitability for 35kV Applications
At 35kV, the fault energy levels, insulation coordination requirements, and expected service life of the installation all favour the armored switchgear configuration. The KYN61-40.5, rated at 40.5kV with short-circuit breaking capacity of 25 kA or 31.5 kA, is designed specifically for this voltage class. Fixed type panels at 35kV exist and are used in some markets, but the 35kV switchgear specification issued by most utilities and engineering consultants for primary substation applications defaults to the withdrawable armored type for the safety and operational reasons outlined above.
Real Project Reference: Tanzania 35kV Substation, January 2023
In January 2023, a lineup of KYN61-40.5 armored switchgear cabinets was commissioned at a substation project in Tanzania. The installation completed a 72-hour continuous energised test immediately after commissioning, recording power frequency withstand voltage at 95 kV/1 min and partial discharge below 10 pC - both exceeding the contractual specification.
Commissioning was completed in five days from unpacking to live energisation, against an industry average of seven days. Protection relay settings were fine-tuned to local grid characteristics prior to handover, and remote installation guidance was provided by the GH technical team using 3D animation walkthroughs, resolving busbar compartment alignment without requiring an in-person site visit.
The project demonstrates what properly specified 35kV switchgear delivers in a real operating environment: performance above specification, faster commissioning, and a commissioning process that places minimal burden on the end customer's engineering team.
KYN61-40.5 armored switchgear 35kV substation Tanzania commissioning project
30-Second Selection Table
Use this table to identify the right configuration for your project. Answer each question and follow the result.
Question 1: Does your installation require continuous operation with no planned full-section outages?
- Yes → Truck type withdrawable switchgear
- No → Either configuration may be suitable; proceed to Question 2
Question 2: Will the circuit breakers require in-service testing or replacement within the asset life?
- Yes → Truck type withdrawable switchgear
- No → Proceed to Question 3
Question 3: Is the installation rated at 35kV, or does it serve a critical load such as a power plant, data centre, or continuous industrial process?
- Yes → Truck type withdrawable switchgear / armored type strongly recommended
- No → Fixed type switchgear may be appropriate; consult your project engineer
If two or more of your answers point to truck type, the withdrawable switchgear configuration is the correct specification for your project. If all three answers point to fixed type, the simpler configuration is worth evaluating - though we recommend reviewing the full-life cost calculation with your team before finalising.
MV HV switchgear cabinet KYN61-40.5 40.5kV withdrawable armored type
Conclusion
The choice between truck-type switchgear and fixed-type switchgear is not simply a question of budget. It is a question of how much a supply interruption costs your operation, how long you expect the installation to remain in service, and what level of personnel protection your project requires.
For the majority of 35kV substation applications - utility distribution, industrial power supply, renewable energy grid connection - the withdrawable switchgear configuration in an armored medium voltage switchgear cabinet delivers lower lifetime cost, greater operational flexibility, and a higher standard of personnel safety than the fixed alternative.
If you are specifying 35kV switchgear for an upcoming project and would like to discuss configuration options, busbar ratings, or protection relay requirements, contact the GH technical team for a detailed review.