Direct Answer

With a limited budget, how should you choose between "installing online monitoring" and "sticking with outage preventive tests"? The answer: the two solve different problems — preventive tests are done during outages and find existing defects; online monitoring runs during operation and catches developing trends. Decide by equipment importance and outage cost: critical, high-outage-cost cubicle groups get online monitoring; general groups keep preventive tests. The mature approach is "preventive tests as the base + online monitoring for critical circuits," not an either/or choice.

At one plant with 120 panels of 10 kV switchgear and a limited budget, the decision framework was applied: 20 critical circuits (main-transformer feeders, important loads) got online monitoring (PD + temperature); 100 general circuits kept the preventive-test interval. Result: in month 8, online monitoring found a rising PD trend on one panel (alert); outage inspection found and treated a contact-box defect early; preventive tests continued covering existing defects. Cost comparison: full online coverage would cost 120 panels; the hybrid covered 20 — 80% budget saved with no reduction in critical-equipment coverage. Conclusion: the decision's core is grading by importance and outage cost, not either/or.

Because:

  • The two tools differ in capability: tests find existing, online catches developing;
  • Outage cost differs: one outage of a critical circuit is expensive (continuous production);
  • Defect-discovery timing differs: the interval between tests is a blind zone; online is real-time;
  • Investment logic differs: full online is expensive; a hybrid has the best value.

Key insight: the decision is not "either/or" but "graded combination." Importance × outage cost — critical circuits online, general circuits tested; budget spent where it matters.

At one plant, a critical busbar panel had no online monitoring and suffered an insulation-breakdown incident between two preventive tests (3 days of production stoppage). Review found the panel was of high importance and high outage cost — an "should-be-online" category that was skipped. Rectification: all critical circuits got online monitoring (PD + temperature); general circuits kept tests. Lesson: saving budget must not skip online coverage for critical circuits — importance grading is the first principle of the decision.

1. Capability Comparison of the Two Approaches

Step one: what each can do.

Outage preventive tests (DL/T 596):

  • State: tests in the de-energized condition;
  • Capabilities: withstand, insulation, DC resistance, dielectric loss, etc.;
  • Finds: existing defects (present, not developing);
  • Frequency: periodic (1–6 years by equipment);
  • Criteria: explicit pass standards (handle when over limit).

Online monitoring:

  • State: continuous monitoring in the energized condition;
  • Capabilities: temperature, PD, insulation trends, etc.;
  • Finds: developing defects (worsening, trend changes);
  • Frequency: real-time continuous;
  • Output: trend alerts, anomaly localization.

Capability comparison:

  • What tests do cannot be replaced online (withstand, etc.);
  • What online does is not covered by tests (the blind zone between tests);
  • Intersection: insulation state (tests measure point values, online measures trends);
  • Complementary logic: existing + developing = full picture.

Key insight: capabilities are complementary, not overlapping. Tests manage the "point" (snapshot), online manages the "line" (continuous trend) — together they form the "plane."

2. Cost and Outage Cost

Step two: how to calculate cost.

Cost composition:

  • Test cost: test labor + outage loss (production stoppage/load reduction);
  • Online cost: equipment purchase + installation + operations;
  • Outage cost: a critical-circuit outage costs far more than the test fee;
  • Total cost: direct fees + indirect loss (outage).

Outage-cost grading:

  • High: main-transformer feeders, important loads (large stoppage loss);
  • Medium: general production circuits (short load reduction);
  • Low: auxiliary circuits (can be de-energized freely);
  • Test impact: outage windows hard to schedule (continuous-production scheduling).

Investment comparison:

  • Full online: full coverage but high cost (waste on non-critical circuits);
  • Full tests: low cost but with a blind zone (risk on critical equipment);
  • Hybrid: critical online + general tested (optimal);
  • Payback view: one accident's loss exceeds years of online investment.

Key insight: cost must look at "outage cost," not the "test fee." One production stoppage on a critical circuit far exceeds online investment — invest where the equipment is important and high-outage-cost.

3. Decision Dimension: Importance × Outage Cost

Step three: how to grade.

Decision matrix:

  • High importance + high outage cost: online mandatory (critical circuits);
  • High importance + low outage cost: online first (high monitoring value);
  • Low importance + high outage cost: online optional (per budget);
  • Low importance + low outage cost: tests suffice (general circuits).

Importance judgment:

  • Supply-continuity requirements (hospitals/data centers/continuous lines);
  • Load class (Class 1 > Class 2 > Class 3);
  • Fault consequences (stoppage/safety/equipment damage);
  • Equipment condition (aging/historical defects/harsh environment).

Outage-cost judgment:

  • Outage loss (stoppage hours × unit output value);
  • Outage difficulty (scheduling windows, approval process);
  • Backup capability (with backup can stop; without, hard);
  • Safety impact (outage-operation risk).

Key insight: the decision matrix is two-dimensional grading. Importance decides "worth installing," outage cost decides "worth online" — matrix positioning makes the budget precise.

4. Combination Strategy

Step four: how to combine.

Mature approach:

  • Tests as the base: all equipment tested per the code's interval (mandatory items kept);
  • Critical circuits online: important + high-cost equipment gets online monitoring;
  • General circuits tested: keep periodic tests (low-cost coverage);
  • Anomaly linkage: online alert → schedule outage verification/repair.

Configuration plan:

  • Critical groups: online monitoring (PD + temperature + insulation trends);
  • General groups: tests primarily (periodic tests + spot infrared);
  • Aging equipment: online first (higher defect probability);
  • Harsh environments: online first (outdoor/high-humidity/high-temperature).

Implementation steps:

  • Step 1: grade the equipment list (importance × outage cost);
  • Step 2: determine the online scope (critical circuits first);
  • Step 3: configure monitoring (PD/temperature per defect type);
  • Step 4: data loop (online + tests analyzed side by side).

Key insight: the combination is "full test coverage + online on the criticals." Mandatory items not skipped, critical circuits online — budget on the edge, risk fully covered.

5. Investment-Payback Perspective

Step five: is the investment worth it.

Payback logic:

  • Accident cost: one critical-equipment failure (stoppage + repair) cost;
  • Online investment: monitoring equipment + installation + operations (several years);
  • Comparison: one accident loss > years of online investment (high-importance equipment);
  • Early-detection value: small defects treated early (far cheaper than major repair).

Quantitative reference:

  • Critical circuits: online investment ≈ 10%–20% of one accident's loss;
  • Early detection: early treatment vs post-fault major repair (1:3–1:10);
  • Downtime: alert-based maintenance vs fault emergency repair (several times shorter);
  • Non-critical circuits: online investment may exceed the benefit (keep tests).

Decision recommendations:

  • High-value equipment: online investment "must be worth it" (prevent accidents);
  • General equipment: test cost "is enough" (control costs);
  • Budget allocation: protect the criticals first, then expand;
  • Data value: monitoring data accumulates (condition assessment/interval optimization).

Key insight: payback looks at "loss avoided." One critical-circuit accident loss far exceeds online investment — preventing accidents is the greatest return.

6. Product Landing: Predictive-Maintenance Scheme

FEXLINK products land the combination strategy:

  • Predictive-Maintenance Scheme: configuration graded by equipment importance (critical circuits online);
  • PD + temperature monitoring: early detection of developing defects;
  • Coordination with tests: side-by-side cross-validation of data;
  • Trend alerts: online alert → schedule outage verification/repair.

Design principle in one sentence: "tests as the base + critical circuits online" — graded combination. Budget on the edge, risk fully covered — equipment health and investment efficiency together.

Graded implementation example (120 panels):

  • Level 1 (20 critical circuits): online monitoring (PD + temperature); in month 8 a rising PD trend was found → outage treatment of a contact-box defect;
  • Level 2 (40 important circuits): test interval + spot infrared inspection;
  • Level 3 (60 general circuits): periodic tests per the code;
  • Cost comparison: full online would cost 120 panels; the hybrid covered 20 — 80% budget saved, critical coverage unchanged.

Combination suggestions by equipment type:

  • Switchgear: critical panels online (PD + temperature) + general panels tested;
  • Transformers: main transformer online (temperature + PD) + distribution transformers tested;
  • Cables: important circuits online (temperature) + general circuits tested;
  • Motors: critical motors online (temperature + vibration) + general motors tested.

7. Common Decision Misconceptions

  1. Either/or thinking: all online or all tested. Consequence: wasted budget or uncovered critical equipment. Correct: graded combination.
  2. Purchase price only: ignoring outage cost. Consequence: critical circuits not monitored when they should be. Correct: cost = total (including outage loss).
  3. Even effort: equal investment across all groups. Consequence: waste on non-critical, shortage on critical. Correct: grade by importance.
  4. Tests stop once online is installed: mandatory items missing. Consequence: existing defects missed. Correct: tests as base, never skipped.
  5. Investment only, no accident accounting: online feels expensive. Consequence: one accident loss far exceeds the investment. Correct: payback view (preventing accidents = return).

Scope and Limitations

This article provides a decision framework for online monitoring vs periodic preventive tests (capability comparison, cost and outage cost, importance × outage-cost matrix, combination strategy, investment-payback perspective) for planning monitoring/test combinations for switchgear and other equipment under budget constraints. Specific equipment grading and online-monitoring configuration must be determined per on-site load class, outage windows, and historical defect conditions; test intervals and criteria follow the current DL/T 596 version; outage tests must be performed by qualified test personnel per procedures. All cases are anonymized (a certain plant) and do not refer to any specific customer.