Pagsusi sa Pag-aplikar sa Load Switch ug Current-Limiting Fuse Combination Apparatus

Isipag-una nga teknikyan sa loop-network power supply ug prefabricated substation operation ug maintenance, nahimong dili ko mapasabot ang pagbag-o sa equipment gihatod sa paglawak sa high-voltage urban. Batasan sa National Power Supply and Consumption Regulations, para sa mga equipment nga adunay higayon nga mas taas kaysa 250kW o 160kVA, ang 10(6)kV high-voltage power supply ug 220/380V step-down mao ang kinahanglan, nagporma og mahimong importante ang loop-network units ug prefabricated substations sa distribution networks.

I. Equipment Structure ug Protection Scheme Selection
(I) Equipment Composition

Ang mga loop-network units nga gi-handle nako adunay duha ka loop cable intervals ug usa ka transformer circuit interval. Ang prefabricated substations nag-integrate sa high-voltage switches, transformers, ug low-voltage devices sa compact, prefabricated sets alang sa indoor/outdoor use. Ang core mao ang protection sa high-voltage switches labi na sa mga short circuits sa transformers.

(II) Protection Scheme Comparison

Sa practice, nagsulay ko og duha ka mga protection methods: circuit breaker ug load switch + current-limiting fuse. Ang latter mao ang mas maayo — simple, cost-effective, ug mas effective alang sa transformers. Ang short-circuit tests mipakita nga ang transformers nanginahanglan og short-circuit clearing sa 20ms aron malihok ang tank explosions; ang current-limiting fuses makapwede niini sa 10ms, bisan ang circuit breakers magdugay ngadto sa ~60ms (relay + operation + arcing time), kini nako gipili ang fuse scheme.

II. Necessity sa Load Switch + Current-Limiting Fuse
(I) Application Advantages

Ang daghang domestic ug foreign loop-network/prefabricated substation projects nga gisulay nako gigamit og load switch + current-limiting fuses. Sila adunay simple structure, mubo nga presyo, ug maayo nga protection alang sa transformers. Ang short-circuit tests (verified on-site) mipakita nga ang fuses clear faults sa 10ms (vs. circuit breakers’ ~60ms), critical aron malihok ang tank explosions.

(II) Cooperative Logic

Ang fuses makapwede mobati ug unbalanced phase operation kon single-phase fusing moadto. Kini nagpasabot nga ang load switches kinahanglan mag-cooperate: ang fuse strikers trigger ang load switch tripping aron three-phase breaking — verified, indispensable coordination.

III. Cooperation Key Points sa Load Switch ug Fuse

Isip isip front-line worker, naka-on sa akong kaalaman ang importansya sa ilang cooperation. Ang IEC420 standard define rules, dividing current into 4 regions (my debugging basis):

(I) Region I (I < Iak)

I_ak (combined appliance rated current) mas bata kaysa sa fuse rated current I_a.nT (gikan sa installation temperature/heat loss). Ang load switches break rated current ug extinguish three-phase arcs — focus sa akong daily inspection.

(II) Region II (Ia.nT< I < 3Ia.nT)

Sa overload, ang fuses bear over-current first. Sa ~2I_a.nT, melts act (but not arc-extinguishing), strikers trigger load switches for three-phase breaking. I test this time-difference logic to avoid protection failure.

(III) Region III (Transfer Current ITC, ~3Ia.nT Start)

Ang fuses can extinguish arcs after action. One three-phase fuse acts first, triggering strikers; load switches extinguish other two-phase currents. The key is transfer current (load switch’s max breaking current at specific power factor, 5I_a.nT - 15I_a.nT), checked during selection/verification.

(IV) Region IV (Current-Limiting Range)

Para sa extreme faults, ang fuses act in the first half-wave to limit fault current peaks; load switches act but don’t break current. I verify this logic in drills for proper operation.

IV. Transfer & Hand-over Current Requirements

These parameters ensure equipment safety, key for my on-site debugging:

(I) Transfer Current

It’s the critical value for function transfer between fuses and load switches. Below it, fuses break one phase, load switches handle the rest. Striker-equipped load switches need transfer current tests (usually > rated current) — a challenge for old equipment, verified per IEC420.

(II) Hand-over Current

It’s the current fully broken by load switches (no fuse participation). For load switches with both strikers and releases, hand-over current tests are needed. If hand-over current > transfer current, transfer tests may be exempt. Release operation reduces fuse loss but increases vacuum load switch costs (adding relays/releases) — trade-offs made per project budgets/conditions.

V. Transformer Protection Suggestions

For load switch + fuse transformer protection, key verifications include:

• Striker Tripping: Check matching of actual and rated transfer currents for safe breaking.

• Over-current Release: Verify actual and rated hand-over currents for reliable operation.

These tasks are mandatory for new projects/old equipment transformations. As a front-line worker, I ensure stable power supply and safe fault handling for downstream users.